Introduce Amount::from_sat_unchecked

As we did for `SignedAmount` add a constructor to the `Amount` type that
does no checks on its argument.

(This is in preparation for enforcing the MAX_MONEY invariant.)

Use the `_unchecked` version in a single unit test. The rest of the unit
tests will be refactored later to minimise the size of this patch.

units/src/amount/signed.rs

@@ -88,9 +88,7 @@ impl SignedAmount {
     /// Caller to guarantee that `satoshi` is within valid range.
     ///
     /// See [`Self::MIN`] and [`Self::MAX_MONEY`].
-    pub const fn from_sat_unchecked(satoshi: i64) -> SignedAmount {
-        SignedAmount(satoshi)
-    }
+    pub const fn from_sat_unchecked(satoshi: i64) -> SignedAmount { SignedAmount(satoshi) }
 
     /// Converts from a value expressing a decimal number of bitcoin to a [`SignedAmount`].
     ///

units/src/amount/tests.rs

@@ -560,9 +560,9 @@ fn from_str() {
 fn to_from_string_in() {
     use super::Denomination as D;
     let ua_str = Amount::from_str_in;
-    let ua_sat = Amount::from_sat;
+    let ua_sat = Amount::from_sat_unchecked;
     let sa_str = SignedAmount::from_str_in;
-    let sa_sat = SignedAmount::from_sat;
+    let sa_sat = SignedAmount::from_sat_unchecked;
 
     assert_eq!("0.5", ua_sat(50).to_string_in(D::Bit));
     assert_eq!("-0.5", sa_sat(-50).to_string_in(D::Bit));

units/src/amount/unsigned.rs

@@ -90,6 +90,11 @@ impl Amount {
     /// ```
     pub const fn to_sat(self) -> u64 { self.0 }
 
+    /// Constructs a new [`Amount`] with satoshi precision and the given number of satoshis.
+    ///
+    /// Caller to guarantee that `satoshi` is within valid range. See [`Self::MAX_MONEY`].
+    pub const fn from_sat_unchecked(satoshi: u64) -> Amount { Self(satoshi) }
+
     /// Converts from a value expressing a decimal number of bitcoin to an [`Amount`].
     ///
     /// # Errors