Codecs could drop leading zeros/ones from constrained integer bytes before constructing the type

[Nicceboy]

Sometimes when decoding constrained integer types, it is acceptable for the codec that there are many leading zeros or ones which do not actually affect for the integer value.

When the constrained integer type is not using Rust integer primitive types directly, but rather the new variable-sized Integer type, decoding could get small performance benefits if those bytes are dropped. This would result into increased usage of the internal isize type rather than allocated BitInt type, particularly on 32-bit platforms.