Various errno handling cleanup

[fhunleth]

No description provided.

[Copilot]

Pull request overview

This PR refactors errno handling in the C NIF layer to centralize errno-to-term translation and to avoid using strerror() strings for exception reasons.

Changes:

• Introduces make_errno_atom/2 to translate errno values (including -errno return codes) into Erlang atoms, with special-cases for existing custom atoms.
• Updates NIF read/write paths to raise exceptions using the new errno atom mapping instead of strerror(...).
• Simplifies make_errno_error/2 by delegating to make_errno_atom/2 (but this changes the error-term shape for “unexpected errors”).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
c_src/nif_utils.c	Adds make_errno_atom/2 and refactors errno error construction logic
c_src/gpio_nif.h	Exposes make_errno_atom/2 in the NIF utilities header
c_src/gpio_nif.c	Uses make_errno_atom/2 for raised exception reasons in read/write NIFs

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