feat: replacing panic, unwrap & unimplemented error outs with syn::Error

[Manudasari265]

Summary of Changes

Audited all relevant proc-macro crates and replaced reachable panic paths with syn::Error diagnostics that point at the offending token in the user's source. Intentionally kept safe internal invariants are marked with // safe-unwrap: comments. Added CI lint script that fails the build on any unguarded panic path in proc-macro crates

Audit Fixes

anchor-derive-space (lang/derive/space)

• Replace unimplemented!() with syn::Error when #[derive(InitSpace)] is applied to a union type
• Replace panic!("Type {ty:?} is not supported") with syn::Error::new_spanned for unsupported field types (e.g. &str, *const T, dyn Trait)

anchor-derive-accounts (lang/derive/accounts)

• No reachable panic paths found - delegates entirely to anchor-syn

anchor-derive-serde (lang/derive/serde)

• Replace .expect() on proc_macro_crate::crate_name("anchor-lang") with syn::Error for missing dependency

anchor-attribute-account (lang/attribute/account)

• Replace panic! with syn::Error when #[derive(ZeroCopyAccessor)] is applied to a non-named-fields struct
• Replace panic!/.expect() with syn::Error for invalid #[accessor] attribute syntax (missing args, empty parens, wrong token)
• Replace panic! with syn::Error for invalid #[zero_copy(...)] arguments (also resolves existing TODO comment)

anchor-attribute-access-control (lang/attribute/access-control)

• Replace .unwrap() with syn::Error when #[access_control(...)] arguments fail to tokenize

anchor-attribute-program (lang/attribute/program)

• Replace unimplemented! in convert_idl_type_to_str for unhandled IdlType variants in declare_program! (also resolves existing TODO comment)
• Replace unimplemented! for unsupported IDL serialization types
• Replace unimplemented! for unsupported IDL repr types

CI Lint

• Added scripts/check-proc-macro-panics.sh - fails if any unguarded panic!/unwrap()/unimplemented!/expect() appears in proc-macro crates; intentionally kept safe invariants are
  exempted via // safe-unwrap: inline comments
• Added proc-macro-panic-lint job to .github/workflows/global-lint.yaml

fixes #4280

[vercel]

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[Manudasari265]

hi @nutafrost PR is ready for review, audited and addressed all the proc-macro crates. kindly let me know if I have missed any or to address any

[jamie-osec]

Can we use https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_methods instead of grepping? This will help catch things locally (at least when people run Clippy)