Update `segwit_weight` and `legacy_weight` to use non-deprecated functions

diff --git a/bitcoin/src/blockdata/block.rs b/bitcoin/src/blockdata/block.rs
index 5725d05b..7558beef 100644
--- a/bitcoin/src/blockdata/block.rs
+++ b/bitcoin/src/blockdata/block.rs
@@ -659,7 +659,7 @@ mod tests {
         assert_eq!(block_base_size(real_decode.transactions()), some_block.len());
         assert_eq!(
             real_decode.weight(),
-            Weight::from_non_witness_data_size(some_block.len().to_u64())
+            Weight::from_vb_unchecked(some_block.len().to_u64())
         );
 
         assert_eq!(serialize(&real_decode), some_block);
diff --git a/bitcoin/src/blockdata/transaction.rs b/bitcoin/src/blockdata/transaction.rs
index 9b79cbf5..51210477 100644
--- a/bitcoin/src/blockdata/transaction.rs
+++ b/bitcoin/src/blockdata/transaction.rs
@@ -139,7 +139,7 @@ internal_macros::define_extension_trait! {
         ///
         /// If the coversion overflows.
         fn legacy_weight(&self) -> Weight {
-            Weight::from_non_witness_data_size(self.base_size().to_u64())
+            Weight::from_vb(self.base_size().to_u64()).unwrap()
         }
 
         /// The weight of the TxIn when it's included in a SegWit transaction (i.e., a transaction
@@ -158,8 +158,8 @@ internal_macros::define_extension_trait! {
         ///
         /// If the coversion overflows.
         fn segwit_weight(&self) -> Weight {
-            Weight::from_non_witness_data_size(self.base_size().to_u64())
-                + Weight::from_witness_data_size(self.witness.size().to_u64())
+            Weight::from_vb(self.base_size().to_u64())
+            .and_then(|w| w.checked_add(Weight::from_wu(self.witness.size().to_u64()))).unwrap()
         }
 
         /// Returns the base size of this input.
diff --git a/units/src/weight.rs b/units/src/weight.rs
index 3d8d257d..4b67a2eb 100644
--- a/units/src/weight.rs
+++ b/units/src/weight.rs
@@ -96,6 +96,7 @@ impl Weight {
     }
 
     /// Constructs a new [`Weight`] from witness size.
+    #[deprecated(since = "TBD", note = "use `from_wu` instead")]
     pub const fn from_witness_data_size(witness_size: u64) -> Self { Weight::from_wu(witness_size) }
 
     /// Constructs a new [`Weight`] from non-witness size.
@@ -103,6 +104,7 @@ impl Weight {
     /// # Panics
     ///
     /// If the conversion from virtual bytes overflows.
+    #[deprecated(since = "TBD", note = "use `from_vb` or `from_vb_unchecked` instead")]
     pub const fn from_non_witness_data_size(non_witness_size: u64) -> Self {
         Weight::from_wu(non_witness_size * Self::WITNESS_SCALE_FACTOR)
     }
@@ -366,6 +368,8 @@ mod tests {
     fn from_vb_unchecked_panic() { Weight::from_vb_unchecked(u64::MAX); }
 
     #[test]
+    #[allow(deprecated)] // tests the deprecated function
+    #[allow(deprecated_in_future)]
     fn from_witness_data_size() {
         let witness_data_size = 1;
         let got = Weight::from_witness_data_size(witness_data_size);
@@ -374,6 +378,8 @@ mod tests {
     }
 
     #[test]
+    #[allow(deprecated)] // tests the deprecated function
+    #[allow(deprecated_in_future)]
     fn from_non_witness_data_size() {
         let non_witness_data_size = 1;
         let got = Weight::from_non_witness_data_size(non_witness_data_size);