…unctions.

This commit significantly refactors the BmpTool to act as a true API
layer over the core bitmap processing logic.

Key changes:
- Modified `BmpTool::load` and `BmpTool::save` in `src/format/bitmap.cpp`
  to delegate more responsibility to the core library functions
  (::CreateMatrixFromBitmap, ::CreateBitmapFromMatrix), reducing
  redundant parsing and serialization logic.
- Removed unused internal formatting helpers from `src/format/`.
- Exposed 24 image manipulation functions (shrink, rotate, greyscale,
  color adjustments, blur, etc.) through the `BmpTool` API in
  `include/bitmap.hpp`. These functions now operate on
  `BmpTool::Bitmap` and return `BmpTool::Result`.
- Implemented these API functions in `src/format/bitmap.cpp`, where they
  wrap calls to the core library, handling data conversion (RGBA for API,
  BGRA for internal matrix) and error propagation.
- Updated `main.cpp` to exclusively use the `BmpTool` API for all
  bitmap operations, serving as an example of API usage.
- Created `tests/test_bmptool_api_manipulations.cpp` with unit tests
  for the newly exposed `BmpTool` image manipulation functions.
- Existing tests for core components (`test_bitmap.cpp`,
  `test_bitmap_file.cpp`) and relevant fuzz tests (`fuzz_bitmap.cpp`,
  `fuzz_bmp_tool_save.cpp`) were reviewed and confirmed/kept.

This refactoring provides a cleaner separation of concerns, with BmpTool
now providing a consistent interface for all bitmap operations.