clean up macro impl_bytesn_repr and remove export

[jayz22]

What

clean up impl_bytesn_repr and remove its macro_export, it was intended as an internal helper macro.

[Copilot]

Pull request overview

This PR makes the impl_bytesn_repr helper macro internal-only (removing its #[macro_export]), and updates internal crypto types to use the cleaned-up internal macro via crate-level macro import.

Changes:

• Remove the exported impl_bytesn_repr/impl_bytesn_repr_without_from_bytes split and keep a single internal impl_bytesn_repr macro (no from_bytes).
• Import macros from bytes into the crate root with #[macro_use] so internal modules can use impl_bytesn_repr! without exporting it.
• Update BN254 and BLS12-381 wrapper types to use impl_bytesn_repr! and drop the old macro import.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
soroban-sdk/src/lib.rs	Imports bytes macros into the crate root to enable internal macro use without exporting.
soroban-sdk/src/crypto/bn254.rs	Switches to impl_bytesn_repr! and removes the old macro import.
soroban-sdk/src/crypto/bls12_381.rs	Switches to impl_bytesn_repr! and removes the old macro import.
soroban-sdk/src/bytes.rs	Consolidates the helper macro and removes #[macro_export] to keep it internal.

[mootz12]

[picky] can we fix the unused deps warnings in the tests?

warning: unused import: `crate::bytesn`
   --> soroban-sdk/src/crypto/bls12_381.rs:810:9
    |
810 |     use crate::bytesn;
    |         ^^^^^^^^^^^^^
    |
    = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

[jayz22]

[picky] can we fix the unused deps warnings in the tests?

fixed. sorry about that