Annotation parser should not split on ',' or '|' inside string literals

[bbopen]

Summary

splitTopLevel in src/tywrap.ts doesn’t track string literal boundaries. Annotations like Literal["a,b"] or Literal["x|y"] are split incorrectly, leading to malformed PythonType parsing and invalid TS types.

Failure mode

• Literal["a,b"] is split into two parts and mapped to "a" and "b" instead of the single literal "a,b".
• Literal["x|y"] is split at |, producing a union that isn’t in the source.

Evidence

• src/tywrap.ts splitTopLevel only tracks bracket/paren depth; it ignores quoted strings.

Proposed fix

• Teach splitTopLevel to recognize quoted string sections and ignore separators inside them.
• Add tests for Literal strings containing commas and pipes.

Acceptance criteria

• Literal annotations with embedded , or | parse correctly.
• Tests cover Literal["a,b"], Literal["x|y"], and nested cases.