Fix correlated subqueries in grouped selects

[pratyushsinghal7]

Fixes #1106

Summary

• retain the first source-row scope for each group so correlated scalar subqueries can resolve outer table aliases
• resolve plain selected columns from that source row while keeping aggregate and grouped expressions on group state
• avoid overwriting non-grouped columns with missing group values
• add regression coverage for the reported grouped correlated subquery

Testing

• bun test --preload ./test/bun-setup.js ./test/test1106.js ./test/test1967.js ./test/test941.js ./test/test416.js (25 passed, 1 skipped)
• full suite: 2189 passed, 213 skipped, 0 failed
• prettier --check src/40select.js src/423groupby.js src/424select.js test/test1106.js
• git diff --check

[mathiasrw]

Thank you!