Update build environment to Alpine, enable GUI support, and refine developer guide
- Migrated Dockerfile base image from Ubuntu 22.04 to Alpine 3.19 for a smaller and faster container.
- Added dependencies for GUI support (SDL2, OpenGL/Mesa, Freetype, etc.) and updated CMake options.
- Enhanced `DEVELOPER_GUIDE.md` with new instructions for GUI builds, updated dependencies, and simplified custom build workflows.
- Addressed Alpine-specific ncurses library path issues in CMake configuration.
- Introduced a `Dockerfile` for setting up a minimal Ubuntu-based build environment with required dependencies.
- Added `docker-build.sh` script to simplify Linux build and test execution using Docker or Podman.
- Updated `DEVELOPER_GUIDE.md` with instructions for using Docker/Podman for Linux builds, including CI/CD integration examples.
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.
