Full-codebase formatting, clang-tidy, and include unification

[hasinoff]

This change applies a comprehensive pass of clang-format and clang-tidy cleanups across the repository, unifies C standard library header inclusions, and introduces automated CI formatting enforcement.

Summary of Changes:

1. Clang-Format:

   • Re-formatted all source files, examples, and tests using standard Google C++ formatting.
   • Formatted kZigzag, kInvZigzag, and kDefaultMatrices in src/quantize.cc with exactly 8 elements per row, protected by // clang-format off / // clang-format on blocks to preserve matrix layout.
   • Kept the large 114k lookup table in src/score_7.cc protected from reformatting.

2. Automated CI Format Check (.github/workflows/ci-format-check.yml):

   • Added a standalone GitHub Actions workflow running RafikFarhad/clang-format-github-action@v7 to enforce clang-format on all .cc and .h files across push and PR events, with automatic PR concurrency cancellation.

3. Clang-Tidy Configuration (.clang-tidy):

   • Added a portable .clang-tidy file enabling standard upstream checks: bugprone-*, google-*, misc-*, modernize-*, performance-*, portability-*, and readability-*.
   • Applied cleanups for namespace closing comments, redundant void arguments, nullptr modernizations, explicit constructors, and unused declarations.

4. Include Cleanup (IWYU pass):

   • Added missing direct headers for used symbols (e.g., <stdlib.h>, <assert.h>, <algorithm>, <vector>).
   • Pruned unused includes across src/ and examples/.
   • Configured IWYU pragma: export in src/sjpegi.h (for simd.h, sjpeg.h, bit_writer.h) and keep pragmas in examples/vjpeg.cc to keep automated include analyzers clean in future PRs.

5. Header Style Unification:

   • Unified all C standard library includes to use the <*.h> style across the codebase (e.g., <stdint.h>, <stdlib.h>, <assert.h>, <math.h>, <limits.h>), matching existing predominant repository usage.

Testing:

• Verified all targets compile cleanly (cmake --build build -j).
• Passed all local test suites with 100% success rate (unit_test, test_cmd, test_png_jpg).
• Clean clang-tidy run across all translation units.
• Verified CI Format Check passes green on GitHub Actions.

[vrabaud]

Hi, thx. How about adding a test to the CI ? E.g. https://github.com/webmproject/libsmpte2094-50/blob/a8ec3fc61b9ed0719b32a198816804dbb3b6da82/.github/workflows/ci-format-check.yml#L13-L22

[skal65535]

Hi, thx. How about adding a test to the CI ? E.g. https://github.com/webmproject/libsmpte2094-50/blob/a8ec3fc61b9ed0719b32a198816804dbb3b6da82/.github/workflows/ci-format-check.yml#L13-L22

yes please!

[hasinoff]

Hi, thx. How about adding a test to the CI ? E.g. https://github.com/webmproject/libsmpte2094-50/blob/a8ec3fc61b9ed0719b32a198816804dbb3b6da82/.github/workflows/ci-format-check.yml#L13-L22

yes please!

Good call, done.

[skal65535]

i don't agree with all the clang formatting (like when semantically-close params are decoupled. e.g. "int width, int height") but there's certainly a value in unified and automated clang-format treatment. submitting.