test: add hardware-independent libuvc regression gate

[andrescera]

What

• Add a hardware-independent CTest regression suite for descriptor parsing, H.264/H.265 negotiation, and stream transfer/error handling.
• Wire the regression suite into CI with exact test-inventory validation and JUnit output.
• Replace the local .omo changelog citation with repo-contained evidence and update README guidance.

Why

The previous CI path built libuvc with BUILD_TEST=OFF and only checked source text, so high-risk parser and streaming regressions could pass without executing assertions. This adds a real camera-free gate that runs in GitHub Actions.

How to verify

cmake -S . -B build/regression \
  -DCMAKE_POLICY_VERSION_MINIMUM=3.5 \
  -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_BUILD_TARGET=Static \
  -DBUILD_SHARED_LIBS=OFF \
  -DBUILD_EXAMPLE=OFF \
  -DBUILD_TEST=OFF \
  -DBUILD_TESTING=ON
cmake --build build/regression --parallel
ctest --test-dir build/regression --show-only=json-v1 | jq -e '.tests | length == 13'
ctest --test-dir build/regression --output-on-failure

Additional local checks run before opening:

actionlint .github/workflows/build.yml

Risks

• The new regression tests are Linux/GNU-linker focused because they use linker wrapping around libusb calls. CI runs them on Ubuntu 22.04 and 24.04.
• The suite is intentionally camera-free. It covers parser, negotiation, and callback error paths, but not physical USB timing or real-device interoperability.