Add benchmarks for core operations, migration edge case tests, improved
buffer I/O tests, and developer guide
- Introduced `test_benchmarks.cc` for performance benchmarking of key
operations in `PieceTable` and `Buffer`, including syntax highlighting
and iteration patterns.
- Added `test_migration_coverage.cc` to provide comprehensive tests for
migration of `Buffer::Rows()` to `PieceTable` APIs, with edge cases,
boundary handling, and consistency checks.
- Enhanced `test_buffer_io.cc` with additional cases for save/load
workflows, file handling, and better integration with the core API.
- Documented architectural details and core concepts in a new
`DEVELOPER_GUIDE.md`. Highlighted design principles, code
organization, and contribution workflows.
Kyle Isom
8ec0d6ac41