Remove GTest dependency, add code coverage, and refactor unit tests and CI pipelines (#744)

- Removes the GTest dependency, replacing it with a minimal custom
framework (`test/framework.*`) that covers only what the tests actually
use — a unified `TEST()` macro with SFINAE-based fixture auto-detection,
`EXPECT_*`/`ASSERT_*` assertions, environments, and setup/teardown.
- `--exclude-perf-tests` flag and substring-based negative filtering
- `MSCCLPP_ENABLE_COVERAGE` CMake option with gcov/lcov; CI uploads to
Codecov
- Merges standalone `test/perf/` into main test targets
- Refactors Azure pipelines to reduce redundancies & make more readable

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Changho Hwang <changhohwang@microsoft.com>

.github/workflows/codeql-analysis.yml

@@ -40,7 +40,7 @@ jobs:
       fail-fast: false
       matrix:
         language: [ 'cpp', 'python' ]
-        version: [ 'cuda11.8', 'cuda12.8' ]
+        version: [ 'cuda11.8', 'cuda12.9' ]
 
     steps:
     - name: Checkout repository
@@ -62,7 +62,7 @@ jobs:
     - name: Build
       run: |
         rm -rf build && mkdir build && cd build
-        cmake -DMSCCLPP_BYPASS_GPU_CHECK=ON -DMSCCLPP_USE_CUDA=ON ..
+        cmake -DMSCCLPP_BYPASS_GPU_CHECK=ON -DMSCCLPP_USE_CUDA=ON -DMSCCLPP_BUILD_TESTS=OFF ..
         make -j4
 
     - name: Perform CodeQL Analysis
@@ -107,7 +107,7 @@ jobs:
     - name: Build
       run: |
         rm -rf build && mkdir build && cd build
-        CXX=/opt/rocm/bin/hipcc cmake -DMSCCLPP_BYPASS_GPU_CHECK=ON -DMSCCLPP_USE_ROCM=ON ..
+        CXX=/opt/rocm/bin/hipcc cmake -DMSCCLPP_BYPASS_GPU_CHECK=ON -DMSCCLPP_USE_ROCM=ON -DMSCCLPP_BUILD_TESTS=OFF ..
         make -j4
 
     - name: Perform CodeQL Analysis