uucore: deduplicate CharByte From implementations using macro

[ppmpreetham]

Summary

Replace repetitive From implementations for CharByte with a reusable macro.

This introduces a new macro impl_from_for_enum! in uucore::macros and uses it
to generate the existing From<char>, From<u8>, and From<&u8> implementations.

Motivation

The previous implementation manually defined multiple From impls for CharByte
that followed an identical pattern. This change removes duplication while keeping
the behavior unchanged.

The macro is designed to be reusable for similar enum patterns elsewhere in the codebase.

Changes

• Added impl_from_for_enum! macro to uucore::macros
• Replaced manual From implementations for CharByte with macro usage
• No functional changes

Example

Before:

impl From<char> for CharByte { ... }
impl From<u8> for CharByte { ... }
impl From<&u8> for CharByte { ... }

After:

impl_from_for_enum!(CharByte:
    char => Char,
    u8 => Byte, ref
);

Notes

• The macro optionally supports From<&T> via , ref
• Maintains full compatibility with existing iterator usage (.map(CharByte::from))

Testing

• No behavior changes; existing tests continue to pass

Checklist

• Code compiles without warnings
• Follows rustfmt
• No clippy warnings
• No functional changes

[sylvestre]

Sorry but why? :)

[ppmpreetham]

It makes the code more readable, and removes redundant impl codes :)

[sylvestre]

sorry but i am not sure it is worse it ? :)

[ppmpreetham]

It actually makes it better !
check this pattern:
https://effective-rust.com/macros.html#:~:text=enum%20Multi,v%2Eclone%28%29%29%3B%20%7D%20%7D%20result%20%7D%20%7D%20%7D