Merge rust-bitcoin/rust-bitcoin#6972: units: Use third person in rustdoc summaries

### units/src/amount/signed.rs
@@ -145,7 +145,7 @@ impl SignedAmount {
         }
     }
 
-    /// Construct a [`SignedAmount`] value from a `u64` satoshi value.
+    /// Constructs a [`SignedAmount`] value from a `u64` satoshi value.
     ///
     /// # Errors
     ///

### units/src/block.rs
@@ -150,14 +150,15 @@ impl BlockHeight {
     #[inline]
     pub const fn to_u32(self) -> u32 { self.0 }
 
-    /// Attempt to subtract two [`BlockHeight`]s, returning [`None`] if overflow occurred.
+    /// Attempts to subtract two [`BlockHeight`]s, returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_sub(self, other: Self) -> Option<BlockHeightInterval> {
         self.to_u32().checked_sub(other.to_u32()).map(BlockHeightInterval)
     }
 
-    /// Attempt to add an interval to this [`BlockHeight`], returning [`None`] if overflow occurred.
+    /// Attempts to add an interval to this [`BlockHeight`], returning [`None`] if overflow
+    /// occurred.
     #[inline]
     #[must_use]
     pub fn checked_add(self, other: BlockHeightInterval) -> Option<Self> {
@@ -273,14 +274,14 @@ impl BlockHeightInterval {
     #[inline]
     pub const fn to_u32(self) -> u32 { self.0 }
 
-    /// Attempt to subtract two [`BlockHeightInterval`]s, returning [`None`] if overflow occurred.
+    /// Attempts to subtract two [`BlockHeightInterval`]s, returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_sub(self, other: Self) -> Option<Self> {
         self.to_u32().checked_sub(other.to_u32()).map(Self)
     }
 
-    /// Attempt to add two [`BlockHeightInterval`]s, returning [`None`] if overflow occurred.
+    /// Attempts to add two [`BlockHeightInterval`]s, returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_add(self, other: Self) -> Option<Self> {
@@ -357,14 +358,14 @@ impl BlockMtp {
         Self::from_u32(u32::from(timestamps[5]))
     }
 
-    /// Attempt to subtract two [`BlockMtp`]s, returning [`None`] if overflow occurred.
+    /// Attempts to subtract two [`BlockMtp`]s, returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_sub(self, other: Self) -> Option<BlockMtpInterval> {
         self.to_u32().checked_sub(other.to_u32()).map(BlockMtpInterval)
     }
 
-    /// Attempt to add an interval to this [`BlockMtp`], returning [`None`] if overflow occurred.
+    /// Attempts to add an interval to this [`BlockMtp`], returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_add(self, other: BlockMtpInterval) -> Option<Self> {
@@ -455,14 +456,14 @@ impl BlockMtpInterval {
         relative::NumberOf512Seconds::from_seconds_ceil(self.to_u32())
     }
 
-    /// Attempt to subtract two [`BlockMtpInterval`]s, returning [`None`] if overflow occurred.
+    /// Attempts to subtract two [`BlockMtpInterval`]s, returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_sub(self, other: Self) -> Option<Self> {
         self.to_u32().checked_sub(other.to_u32()).map(Self)
     }
 
-    /// Attempt to add two [`BlockMtpInterval`]s, returning [`None`] if overflow occurred.
+    /// Attempts to add two [`BlockMtpInterval`]s, returning [`None`] if overflow occurred.
     #[inline]
     #[must_use]
     pub fn checked_add(self, other: Self) -> Option<Self> {

### units/src/locktime/relative/mod.rs
@@ -427,7 +427,7 @@ impl NumberOfBlocks {
     #[inline]
     pub const fn from_count(blocks: u16) -> Self { Self(blocks) }
 
-    /// Express the [`NumberOfBlocks`] as a count of blocks.
+    /// Expresses the [`NumberOfBlocks`] as a count of blocks.
     #[inline]
     #[must_use]
     pub const fn to_count(self) -> u16 { self.0 }
@@ -542,7 +542,7 @@ impl NumberOf512Seconds {
     #[inline]
     pub const fn from_512_second_intervals(intervals: u16) -> Self { Self(intervals) }
 
-    /// Express the [`NumberOf512Seconds`] as an integer number of 512-second intervals.
+    /// Expresses the [`NumberOf512Seconds`] as an integer number of 512-second intervals.
     #[inline]
     #[must_use]
     pub const fn to_512_second_intervals(self) -> u16 { self.0 }