feat(testing): add JUnit formatter for TestReport

[diiviikk5]

Closes #1567

Summary

Add a deterministic JUnitFormatter to mofa-testing so TestReport can be exported as JUnit XML for CI systems and test-report consumers.

What Changed

• added JUnitFormatter to the report layer
• exported it through tests/src/report/mod.rs and tests/src/lib.rs
• mapped TestReport into a single testsuite
• mapped each TestCaseResult into a testcase
• encoded failures with <failure>
• encoded skipped tests with <skipped/>
• included metadata as <properties> when present
• escaped XML-sensitive content for stable output

Why

mofa-testing already had JSON and text output, and Markdown is being added separately, but there was still no native JUnit XML path for CI tooling. This PR fills that gap without changing the existing report model.

Testing

Ran:

cargo test -p mofa-testing --test report_tests