Improve Semaphore test report grouping and summaries

[DenBond7]

Problem

Semaphore published each test job under its full job name. This split instrumentation results across matrix shards and prevented tests from the same class from being grouped together.

The generated reports were also unavailable to Semaphore MCP, and the workflow Report tab remained empty.

Changes

• Group all instrumentation results under a stable Instrumentation tests report name.
• Keep unit tests in a separate JUnit tests group.
• Generate MCP-optimized summaries for job and pipeline reports.
• Generate a workflow Markdown report containing:
  • overall test status and counters;
  • statistics by test group;
  • failed and errored tests;
  • the 10 slowest tests;
  • branch and commit information.
• Publish the Markdown report as .semaphore/REPORT.md.

Closes #3290

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Tests (delete all except exactly one):

• Does not need tests (refactor only, docs or internal changes)

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities

[sosnovsky]

nice improvement 👍