docs: Add GitHub issue references to TODO comments

[perigrin]

Summary

Added issue references to TODO markers in test files for better tracking:

• Grammar: Method calls with arithmetic operators cause parser timeout #577: Method calls with arithmetic operators cause parser timeout
• Precedence parsing fails on complex real-world classes #578: Precedence parsing fails on complex real-world classes

Changes

• : Reference Grammar: Method calls with arithmetic operators cause parser timeout #577 instead of State variables create UnboundVariable nodes with no visitor #559
• : Reference Precedence parsing fails on complex real-world classes #578 for both tests 7 and 9

Why

These issues were created to track the specific problems documented in the TODO markers. The references provide better context and tracking for future work on resolving these grammar/parsing issues.

Related

• State variables create UnboundVariable nodes with no visitor #559 - Where these TODOs were added
• Grammar: Method calls with arithmetic operators cause parser timeout #577 - New issue for method call arithmetic ambiguity
• Precedence parsing fails on complex real-world classes #578 - New issue for precedence parsing failures