refactor: move unwrap_optional to bytecode module

[zharinov]

Summary

• Add is_optional() helper to TypeDef for checking Optional wrapper types
• Add unwrap_optional() to QTypeTable that returns (inner_type, is_optional) tuple
• Update typescript.rs to use the public API instead of private implementation
• Alphabetize module imports in lib.rs

This refactor moves the optional-unwrapping logic from typegen into the bytecode module where it can be reused by other consumers.

Test plan

• All existing tests pass (cargo test -p plotnik-lib)