Use From in map_to_range

In an effort to remove unnecessary casts use `u128::from` to convert
from `u64`s. Leave the cast to `u64` in there because it is right after
a shift right and is brain-dead obvious.

bitcoin/src/bip158.rs

@@ -362,7 +362,7 @@ impl GcsFilterReader {
 }
 
 /// Fast reduction of hash to [0, nm) range.
-fn map_to_range(hash: u64, nm: u64) -> u64 { ((hash as u128 * nm as u128) >> 64) as u64 }
+fn map_to_range(hash: u64, nm: u64) -> u64 { ((u128::from(hash) * u128::from(nm)) >> 64) as u64 }
 
 /// Golomb-Rice encoded filter writer.
 pub struct GcsFilterWriter<'a, W> {