[AddPkg] c3fmt

[WeirdGumi]

Packages to add

• c3fmt: A customizable code formatter for the C3 language

Upstream

• c3fmt: https://github.com/lmichaudel/c3fmt

Why
Provides a dedicated formatter for the C3 language, filling a gap in its ecosystem. It is bundled with the official c3c prebuilt releases, making it a trustworthy choice.

Potential Dependencies
c3fmt:

• musl tree-sitter
• c3c

Additional context
https://github.com/WeirdGumi/eweos-packages/tree/c3fmt