Fix read_file inline block comment headers

[AmirTlinov]

Fixes #9828

Problem

• Inline /* does not enter block-comment state, so header lines are missed.
• /* ... */ code is misclassified as a header comment.

Solution

• Track block-comment state per line when collecting indentation records.
• Treat inline /* as starting comment state for subsequent lines, but not as a header itself.
• Add two unit tests for the above cases.

Testing

• just fmt
• just fix -p codex-core
• cargo test -p codex-core
• cargo test --all-features (flaked once on read_file_tools_run_in_parallel; rerun passed)
• cargo test --all-features -p codex-core --test all suite::tool_parallelism::read_file_tools_run_in_parallel

[etraut-openai]

There is already a PR posted for this issue: #9829.