Fix: Guard against negative runtime values in test results

[Hell1213]

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**Fixes ** : #1072

Problem
TestResult.runtime stores the value of runTime from CCExtractorTester without validation. CCExtractorTester can report negative values due to a timestamp calculation bug in that tool. These invalid values were written directly to the database and displayed on test result pages.

Fix
Added input validation in finish_type_request() before constructing the TestResult record. Negative values are clamped to 0 and a warning is logged with the test ID and original value for diagnostic purposes.

Files Changed
mod_ci/controllers.py: validation added in finish_type_request()
tests/test_ci/test_negative_runtime_fix.py: comprehensive test suite

Testing
All existing tests pass
Added 5 test cases covering negative, positive, invalid, zero, and missing runtime values
Verified proper warning logging and value clamping

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud