Use _u32 in FeeRate constructor instead of _unchecked

When constructing an `Amount` it was observed recently that a `u32` is
often big enough. For the same reason we can use a `u32` to construct a
fee rate instead of overflowing.

Use `_u32`in the constructor and remove the panic.

bitcoin/src/blockdata/script/tests.rs

@@ -751,7 +751,7 @@ fn default_dust_value() {
     assert!(script_p2wpkh.is_p2wpkh());
     assert_eq!(script_p2wpkh.minimal_non_dust(), Amount::from_sat_u32(294));
     assert_eq!(
-        script_p2wpkh.minimal_non_dust_custom(FeeRate::from_sat_per_vb_unchecked(6)),
+        script_p2wpkh.minimal_non_dust_custom(FeeRate::from_sat_per_vb_u32(6)),
         Some(Amount::from_sat_u32(588))
     );
 
@@ -765,7 +765,7 @@ fn default_dust_value() {
     assert!(script_p2pkh.is_p2pkh());
     assert_eq!(script_p2pkh.minimal_non_dust(), Amount::from_sat_u32(546));
     assert_eq!(
-        script_p2pkh.minimal_non_dust_custom(FeeRate::from_sat_per_vb_unchecked(6)),
+        script_p2pkh.minimal_non_dust_custom(FeeRate::from_sat_per_vb_u32(6)),
         Some(Amount::from_sat_u32(1092))
     );
 }

bitcoin/src/psbt/mod.rs

@@ -130,7 +130,7 @@ impl Psbt {
     /// 1000 sats/vByte. 25k sats/vByte is obviously a mistake at this point.
     ///
     /// [`extract_tx`]: Psbt::extract_tx
-    pub const DEFAULT_MAX_FEE_RATE: FeeRate = FeeRate::from_sat_per_vb_unchecked(25_000);
+    pub const DEFAULT_MAX_FEE_RATE: FeeRate = FeeRate::from_sat_per_vb_u32(25_000);
 
     /// An alias for [`extract_tx_fee_rate_limit`].
     ///

units/src/fee_rate/mod.rs

@@ -49,10 +49,10 @@ impl FeeRate {
     /// Minimum fee rate required to broadcast a transaction.
     ///
     /// The value matches the default Bitcoin Core policy at the time of library release.
-    pub const BROADCAST_MIN: FeeRate = FeeRate::from_sat_per_vb_unchecked(1);
+    pub const BROADCAST_MIN: FeeRate = FeeRate::from_sat_per_vb_u32(1);
 
     /// Fee rate used to compute dust amount.
-    pub const DUST: FeeRate = FeeRate::from_sat_per_vb_unchecked(3);
+    pub const DUST: FeeRate = FeeRate::from_sat_per_vb_u32(3);
 
     /// Constructs a new [`FeeRate`] from satoshis per virtual bytes.
     ///
@@ -66,8 +66,9 @@ impl FeeRate {
         Some(FeeRate::from_sat_per_kwu(sat_vb.checked_mul(1000 / 4)?))
     }
 
-    /// Constructs a new [`FeeRate`] from satoshis per virtual bytes without overflow check.
+    /// Constructs a new [`FeeRate`] from satoshis per virtual bytes.
-    pub const fn from_sat_per_vb_unchecked(sat_vb: u64) -> Self {
+    pub const fn from_sat_per_vb_u32(sat_vb: u32) -> Self {
+        let sat_vb = sat_vb as u64; // No `Into` in const context.
         FeeRate::from_sat_per_kwu(sat_vb * (1000 / 4))
     }
 
@@ -304,15 +305,14 @@ mod tests {
     }
 
     #[test]
-    fn from_sat_per_vb_unchecked() {
+    fn from_sat_per_vb_u32() {
-        let fee_rate = FeeRate::from_sat_per_vb_unchecked(10);
+        let fee_rate = FeeRate::from_sat_per_vb_u32(10);
         assert_eq!(FeeRate::from_sat_per_kwu(2500), fee_rate);
     }
 
     #[test]
     #[cfg(debug_assertions)]
-    #[should_panic = "attempt to multiply with overflow"]
+    fn from_sat_per_vb_u32_cannot_panic() { FeeRate::from_sat_per_vb_u32(u32::MAX); }
-    fn from_sat_per_vb_unchecked_panic() { FeeRate::from_sat_per_vb_unchecked(u64::MAX); }
 
     #[test]
     fn raw_feerate() {