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>

docker/base-dev-x.dockerfile

@@ -7,13 +7,38 @@ LABEL org.opencontainers.image.source=https://github.com/microsoft/mscclpp
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
         htop \
-        lcov \
         vim \
         && \
     apt-get autoremove -y && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /tmp/*
 
+# Install lcov 2.2
+RUN LCOV_VERSION="2.2" && \
+    apt-get update && \
+    apt-get install -y --no-install-recommends \
+        cpanminus \
+        gcc \
+        make \
+        perl \
+        && \
+    cpanm --notest \
+        Capture::Tiny \
+        DateTime \
+        JSON::XS \
+        Memory::Process \
+        TimeDate \
+        && \
+    cd /tmp && \
+    curl -L https://github.com/linux-test-project/lcov/releases/download/v${LCOV_VERSION}/lcov-${LCOV_VERSION}.tar.gz -o lcov.tar.gz && \
+    tar xzf lcov.tar.gz && \
+    cd lcov-${LCOV_VERSION} && \
+    make install && \
+    cd / && rm -rf /tmp/lcov* && \
+    apt-get autoremove -y && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/* /tmp/*
+
 # Install CMake 3.26.4
 RUN OS_ARCH=$(uname -m) && \
     CMAKE_VERSION="3.26.4" && \
@@ -47,7 +72,8 @@ RUN target_type=$(echo $TARGET | sed 's/\.[0-9]*$//') && \
         export CUPY_INSTALL_USE_HIP=1 && export ROCM_HOME=/opt/rocm; \
     fi && \
     pip install --no-cache-dir --upgrade pip && \
-    pip install --no-cache-dir -r python/requirements_${target_type}.txt
+    pip install --no-cache-dir -r python/requirements_${target_type}.txt && \
+    pip install --no-cache-dir coverage xlsxwriter
 
 # Cleanup
 RUN rm -rf /tmp/mscclpp