Adopt a formatter / style guide for native code to establish consistency

[traeok]

Is your feature or enhancement request related to a problem or limitation? Please describe

Currently there are a mixture of code styles in the Metal C and C++ code, including different casing for names (snake_case, camelCase).

Describe your enhancement idea

Implement a style guide to establish consistent naming, spacing and code structure. If it works with our project, clang-tidy supports style presets that we could enforce as a baseline.

If clang-tidy is unavailable on the client (as our code only compiles w/ xlc & xlclang on z/OS), find and implement another formatter for the C++ and Metal C code to establish consistent style.

Provide any additional context

Came up in #729 discussion

[traeok]

• Add style suggestions to AGENTS.md
• Use snake_case in native code
• Investigate gating z/OS specific logic under macros to allow compiling in a local env - this would allow clang-tidy to work off platform