Add C header nullability annotations

[Jesssullivan]

Goal

Improve Swift/Objective-C diagnostics for include/zig_notify.h without changing the stable C ABI.

Context

The current header is plain C and works for C consumers. Apple interop would benefit from carefully scoped nullability annotations so Swift/ObjC users get clearer import behavior.

Docs: https://transscendsurvival.org/zig-notify/guides/apple-interop/

Scope

• Audit pointer parameters in include/zig_notify.h for nullability annotations that do not change ABI.
• Keep title and app_name non-null in docs unless behavior changes.
• Keep body nullable for title-only notifications.
• Update README/docs generated from the header.

Validation

• zig build test
• zig build example
• python3 scripts/gen_docs.py

[snakefood3232]

I understand the need to enhance Swift/Objective-C diagnostics in include/zig_notify.h by adding nullability annotations without affecting the stable C ABI. I'd handle this by auditing pointer parameters to add the required annotations and updating the documentation accordingly, ensuring non-null for title and app_name while keeping body nullable. I can have a PR ready within 2 days. I've worked with C/Objective-C interop and nullability annotations in similar projects before.

[Jesssullivan]

@snakefood3232 Hey there, thanks for the reach out!

That'd be lovely; I am juggling a few of these interop libraries trying to get things out and available, a hand with this would be welcome.