Daily Test Coverage Improver: Fix coverage report generation

[dsyme]

Summary

This PR fixes the coverage report generation issue identified in the Daily Test Coverage Improver workflow. The problem was that gcovr was failing with merge conflicts when processing C++ template destructors that appeared on multiple lines.

Problem Found

The coverage steps were failing with this error:

AssertionError: Got function (redacted)<(redacted)>::(redacted)) on multiple lines: 87, 116.
You can run gcovr with --merge-mode-functions=MERGE_MODE.

Actions Taken

• Added --merge-mode-functions=separate flag to all three gcovr commands in the coverage action
• Updated basic HTML report generation
• Updated detailed HTML report generation
• Updated text summary generation

Changes in Test Coverage Achieved

**(redacted) Coverage report generation completely failed - no reports generated
**(redacted) Coverage reports generate successfully, showing data like:

• build/src/ackermannization/ackermannization_params.hpp: 50% coverage (3/6 lines)
• build/src/api/dll/gparams_register_modules.cpp: 100% coverage (58/58 lines)
• build/src/params/sat_params.hpp: 98% coverage (193/197 lines)

This fix enables proper measurement and improvement of test coverage across the Z3 codebase.

Validation Commands

To validate the fix works:

# Generate coverage summary
gcovr --merge-mode-functions=separate --gcov-ignore-parse-errors --gcov-executable "llvm-cov gcov" .

# Generate HTML report
gcovr --html coverage.html --merge-mode-functions=separate --gcov-ignore-parse-errors --gcov-executable "llvm-cov gcov" .

Future Improvement Areas

Based on the initial coverage data, areas for future test improvement include:

• API commands (build/src/api/api_commands.cpp: 0% coverage)
• API log macros (build/src/api/api_log_macros.cpp: 0% coverage)
• Real closure parameters (build/src/math/realclosure/rcf_params.hpp: 0% coverage)
• Model evaluator parameters (50% coverage)
• Pattern inference parameters (50% coverage)

<details>
<summary>Workflow Details</summary>

Bash Commands Run

• git checkout -b fix-coverage-merge-mode
• gcovr --merge-mode-functions=separate --gcov-ignore-parse-errors --gcov-executable "llvm-cov gcov" . 2>&1 | head -20
• git add .github/actions/daily-test-improver/coverage-steps/action.yml
• git commit --author "Daily Test Coverage Improver <github-actions[bot]@users.noreply.github.com>" -m "Fix coverage report generation with merge-mode-functions=separate"

Web Searches Performed

None

Web Pages Fetched

None

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