test(tools): add tests for FileReadTool

[charanpool]

 ## Summary
 Adds unit tests for `FileReadTool` which previously had no test coverage.
 
 ## Tests Added
 - Basic file reading
 - Constructor path initialization
 - Line offset and limit features
 - Error handling (file not found, no path, invalid range)
 
 ## Checklist
 - [x] Tests pass locally (`uv run pytest`)
 - [x] Pre-commit checks pass
 - [x] No external dependencies required

---

Note

Introduces initial test coverage for FileReadTool validating core read behavior and edge cases.

• Verifies reading entire files and using constructor-provided file_path
• Tests start_line and line_count slicing (including single-line and mid-file ranges)
• Covers error cases: missing file_path, nonexistent file, and start_line beyond file length

^{Written by Cursor Bugbot for commit 33d813c. This will update automatically on new commits. Configure here.}