simple_config: factor out self.decimal_point and self.get_decimal_point() in favor of self.BTC_AMOUNTS_DECIMAL_POINT

diff --git a/electrum/gui/qml/qeconfig.py b/electrum/gui/qml/qeconfig.py
index 9609289..caa1509 100644
--- a/electrum/gui/qml/qeconfig.py
+++ b/electrum/gui/qml/qeconfig.py
@@ -387,4 +387,4 @@ class QEConfig(AuthMixin, QObject):
 
     @pyqtSlot('quint64', result=float)
     def satsToUnits(self, satoshis):
-        return satoshis / pow(10, self.config.decimal_point)
+        return satoshis / pow(10, self.config.BTC_AMOUNTS_DECIMAL_POINT)
diff --git a/electrum/gui/qt/main_window.py b/electrum/gui/qt/main_window.py
index ff860f3..f7c1ec9 100644
--- a/electrum/gui/qt/main_window.py
+++ b/electrum/gui/qt/main_window.py
@@ -1005,7 +1005,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger, QtEventListener):
         return self.config.format_fee_rate(fee_rate)
 
     def get_decimal_point(self):
-        return self.config.get_decimal_point()
+        return self.config.BTC_AMOUNTS_DECIMAL_POINT
 
     def base_unit(self):
         return self.config.get_base_unit()
diff --git a/electrum/gui/qt/settings_dialog.py b/electrum/gui/qt/settings_dialog.py
index ca7fba8..43cfd0d 100644
--- a/electrum/gui/qt/settings_dialog.py
+++ b/electrum/gui/qt/settings_dialog.py
@@ -97,7 +97,7 @@ class SettingsDialog(QDialog, QtEventListener):
         nz_label = HelpLabel.from_configvar(self.config.cv.BTC_AMOUNTS_FORCE_NZEROS_AFTER_DECIMAL_POINT)
         nz = QSpinBox()
         nz.setMinimum(0)
-        nz.setMaximum(self.config.decimal_point)
+        nz.setMaximum(self.config.BTC_AMOUNTS_DECIMAL_POINT)
         nz.setValue(self.config.num_zeros)
         if not self.config.cv.BTC_AMOUNTS_FORCE_NZEROS_AFTER_DECIMAL_POINT.is_modifiable():
             for w in [nz, nz_label]: w.setEnabled(False)
@@ -205,7 +205,7 @@ class SettingsDialog(QDialog, QtEventListener):
             if self.config.get_base_unit() == unit_result:
                 return
             self.config.set_base_unit(unit_result)
-            nz.setMaximum(self.config.decimal_point)
+            nz.setMaximum(self.config.BTC_AMOUNTS_DECIMAL_POINT)
             self.app.refresh_tabs_signal.emit()
             self.app.update_status_signal.emit()
             self.app.refresh_amount_edits_signal.emit()
diff --git a/electrum/gui/text.py b/electrum/gui/text.py
index 6417034..32da41c 100644
--- a/electrum/gui/text.py
+++ b/electrum/gui/text.py
@@ -615,7 +615,7 @@ class ElectrumGui(BaseElectrumGui, EventListener):
             x = Decimal(text)
         except Exception:
             return None
-        power = pow(10, self.config.get_decimal_point())
+        power = pow(10, self.config.BTC_AMOUNTS_DECIMAL_POINT)
         return int(power * x)
 
     def read_invoice(self):
diff --git a/electrum/payment_identifier.py b/electrum/payment_identifier.py
index f7f0b53..a71b1bf 100644
--- a/electrum/payment_identifier.py
+++ b/electrum/payment_identifier.py
@@ -557,7 +557,7 @@ class PaymentIdentifier(Logger):
             raise Exception("Amount is empty")
         if parse_max_spend(x):
             return x
-        p = pow(10, self.config.get_decimal_point())
+        p = pow(10, self.config.BTC_AMOUNTS_DECIMAL_POINT)
         try:
             return int(p * Decimal(x))
         except InvalidOperation:
diff --git a/electrum/plugins/bitbox02/bitbox02.py b/electrum/plugins/bitbox02/bitbox02.py
index 2e0c5ec..ead4d8d 100644
--- a/electrum/plugins/bitbox02/bitbox02.py
+++ b/electrum/plugins/bitbox02/bitbox02.py
@@ -518,7 +518,7 @@ class BitBox02Client(HardwareClientBase):
 
         format_unit = bitbox02.btc.BTCSignInitRequest.FormatUnit.DEFAULT
         # Base unit is configured to be "sat":
-        if self.config.get_decimal_point() == 0:
+        if self.config.BTC_AMOUNTS_DECIMAL_POINT == 0:
             format_unit = bitbox02.btc.BTCSignInitRequest.FormatUnit.SAT
 
         sigs = self.bitbox02_device.btc_sign(
diff --git a/electrum/plugins/trezor/trezor.py b/electrum/plugins/trezor/trezor.py
index 456cd25..9487707 100644
--- a/electrum/plugins/trezor/trezor.py
+++ b/electrum/plugins/trezor/trezor.py
@@ -324,11 +324,11 @@ class TrezorPlugin(HW_PluginBase):
         raise ValueError('unexpected txin type: {}'.format(electrum_txin_type))
 
     def get_trezor_amount_unit(self):
-        if self.config.decimal_point == 0:
+        if self.config.BTC_AMOUNTS_DECIMAL_POINT == 0:
             return AmountUnit.SATOSHI
-        elif self.config.decimal_point == 2:
+        elif self.config.BTC_AMOUNTS_DECIMAL_POINT == 2:
             return AmountUnit.MICROBITCOIN
-        elif self.config.decimal_point == 5:
+        elif self.config.BTC_AMOUNTS_DECIMAL_POINT == 5:
             return AmountUnit.MILLIBITCOIN
         else:
             return AmountUnit.BITCOIN
diff --git a/electrum/simple_config.py b/electrum/simple_config.py
index 93621c6..32638bd 100644
--- a/electrum/simple_config.py
+++ b/electrum/simple_config.py
@@ -217,12 +217,10 @@ class SimpleConfig(Logger):
         self._check_dependent_keys()
 
         # units and formatting
-        # FIXME is this duplication (dp, nz, post_sat, thou_sep) due to performance reasons??
-        self.decimal_point = self.BTC_AMOUNTS_DECIMAL_POINT
         try:
-            decimal_point_to_base_unit_name(self.decimal_point)
+            decimal_point_to_base_unit_name(self.BTC_AMOUNTS_DECIMAL_POINT)
         except UnknownBaseUnit:
-            self.decimal_point = DECIMAL_POINT_DEFAULT
+            self.BTC_AMOUNTS_DECIMAL_POINT = DECIMAL_POINT_DEFAULT
         self.num_zeros = self.BTC_AMOUNTS_FORCE_NZEROS_AFTER_DECIMAL_POINT
         self.amt_precision_post_satoshi = self.BTC_AMOUNTS_PREC_POST_SAT
         self.amt_add_thousands_sep = self.BTC_AMOUNTS_ADD_THOUSANDS_SEP
@@ -530,7 +528,7 @@ class SimpleConfig(Logger):
         return format_satoshis(
             amount_sat,
             num_zeros=self.num_zeros,
-            decimal_point=self.decimal_point,
+            decimal_point=self.BTC_AMOUNTS_DECIMAL_POINT,
             is_diff=is_diff,
             whitespaces=whitespaces,
             precision=precision,
@@ -545,15 +543,11 @@ class SimpleConfig(Logger):
         return format_fee_satoshis(fee_rate/1000, num_zeros=self.num_zeros) + f" {util.UI_UNIT_NAME_FEERATE_SAT_PER_VBYTE}"
 
     def get_base_unit(self):
-        return decimal_point_to_base_unit_name(self.decimal_point)
+        return decimal_point_to_base_unit_name(self.BTC_AMOUNTS_DECIMAL_POINT)
 
     def set_base_unit(self, unit):
         assert unit in base_units.keys()
-        self.decimal_point = base_unit_name_to_decimal_point(unit)
-        self.BTC_AMOUNTS_DECIMAL_POINT = self.decimal_point
-
-    def get_decimal_point(self):
-        return self.decimal_point
+        self.BTC_AMOUNTS_DECIMAL_POINT = base_unit_name_to_decimal_point(unit)
 
     def get_nostr_relays(self) -> Sequence[str]:
         relays = []