embassy-stm32: Simplify time

- Remove unused `MilliSeconds`, `MicroSeconds`, and `NanoSeconds` types
- Remove `Bps`, `KiloHertz`, and `MegaHertz` types that were only used
for converting to `Hertz`
- Replace all instances of `impl Into<Hertz>` with `Hertz`
- Add `hz`, `khz`, and `mhz` methods to `Hertz`, as well as
free function shortcuts
- Remove `U32Ext` extension trait

embassy-stm32/src/i2c/v1.rs

@@ -22,15 +22,12 @@ pub struct I2c<'d, T: Instance> {
 }
 
 impl<'d, T: Instance> I2c<'d, T> {
-    pub fn new<F>(
+    pub fn new(
         _peri: impl Unborrow<Target = T> + 'd,
         scl: impl Unborrow<Target = impl SclPin<T>> + 'd,
         sda: impl Unborrow<Target = impl SdaPin<T>> + 'd,
-        freq: F,
-    ) -> Self
-    where
-        F: Into<Hertz>,
-    {
+        freq: Hertz,
+    ) -> Self {
         unborrow!(scl, sda);
 
         T::enable();