ci: add ccache/sccache compilation caching to speed up CI builds (#360)

* ci: add ccache/sccache compilation caching to speed up CI builds

- Use hendrikmuhs/ccache-action@v1.2 for Linux/macOS/iOS/Android/clang-tidy
  (auto-installs ccache, manages cache, sets env vars, shows stats)
- Use mozilla-actions/sccache-action@v0.0.9 for Windows (MSVC compatible)
- Add CMAKE_C/CXX_COMPILER_LAUNCHER to all CMake build steps
- Exclude wheel build and nightly coverage workflows per decision

* ci: switch MacOS & Linux build from Unix Makefiles to Ninja generator

- Replace CMAKE_GENERATOR='Unix Makefiles' with 'Ninja' in pip build
- Replace 'make unittest -j' with 'cmake --build --target unittest --parallel'
- Add '-G Ninja' to C++ and C example cmake configure steps
- Replace 'make -j' with 'cmake --build --parallel' for examples
- Aligns with Windows and Android workflows which already use Ninja

* ci: enable parallel ctest execution with -j and --timeout

- Use CMake ProcessorCount module to detect available CPU cores
- Add -j ${NPROC} to ctest command for parallel test execution
- Add --timeout 300 to prevent individual tests from hanging CI
- Fallback to NPROC=1 when ProcessorCount returns 0
- iOS target unchanged (build-only, no test execution)

* Revert "ci: enable parallel ctest execution with -j and --timeout"

This reverts commit d196dac5f17b1f7cae443360c88bbd8c935dc145.

* fix(ci): remove sccache from Windows, fix cmake.define quote issues

Windows (05-windows-build.yml):
- Remove mozilla-actions/sccache-action: sccache incompatible with MSVC /FS flag
- Remove SCCACHE_GHA_ENABLED env var
- Remove CMAKE_C/CXX_COMPILER_LAUNCHER=sccache from build steps
- Remove 'Show sccache statistics' step
- MSVC /FS (global PDB concurrency flag) causes fatal C1041 when used with sccache

MacOS & Linux (03-macos-linux-build.yml):
- Fix cmake.define values: remove extra quotes around 'ccache' and 'ON'
- Bare values required: cmake.define.FOO=bar not cmake.define.FOO="bar"

* feat: cache key with platform and os

* ci: add compiler to ccache key to avoid cache pollution

* ci: optimize cache usage to reduce bloat

- Add max-size limits to all ccache configs (150M general, 300M Android,
  100M clang-tidy) to prevent unbounded cache growth
- Remove redundant iOS full build directory cache (~1.2 GB) since ccache
  already handles incremental compilation
- Fix iOS protoc cache key to use thirdparty/protobuf/** instead of
  src/**, avoiding unnecessary cache misses on business code changes

* ci: trigger CI run