registerDecls swallows its options parameter

[nazarhussain]

Context

Noted while reviewing #59. registerDecls(decls, options) accepts a comptime options parameter but discards it (_ = options;), while internally passing a hardcoded .{} as the options to createCallback. The parameter is dead weight in a public signature — callers can pass anything and it silently does nothing.

Proposal

Either:

• forward options (or a per-decl subset of it) to createCallback so callers can use arg/return hints (ArgHint, returns hints) with registerDecls, or
• remove/document the parameter as reserved until there is a concrete design for it.

Ref: src/register_decls.zig