docs: refresh README and testing guidance

[ryanbarlow97]

Document JUnit 4 and the absence of a coverage gate; move optional plugin API contract instructions into Docs.

Follows the README layout and documentation ownership rules in TF-Minecraft/Docs. Related guide updates: TF-Minecraft/Docs#110.

Validation: git diff --check; README links, source paths and anchors checked against the task worktrees. Feature and test claims checked against current source and build configuration. Plugin/runtime suites were not rerun for these documentation edits.

[coderabbitai]

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• Run ID: 348c1fa7-4227-4137-9ddb-001a0c471d9a

📥 Commits

Reviewing files that changed from the base of the PR and between 5ae0cfb and b3142e3.

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• README.md

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Updated the testing guidance to describe JUnit, Mockito and MockBukkit coverage, Surefire results, JaCoCo reports and uploaded build artifacts.
  • Clarified that the standard test suite does not require private plugin JARs or a running Paper server.
  • Added a reference to guidance for optional ItemsAdder and MMOItems adapter contract tests.

Walkthrough

The README Tests section now summarises the ordinary test suite, report locations, workflow uploads, and optional adapter contract tests.

Changes

Testing documentation

Layer / File(s)	Summary
Test suite guidance README.md	The Tests section describes JUnit 4, Mockito and MockBukkit coverage, Surefire results, JaCoCo reports, workflow uploads, and the absence of a minimum coverage gate. It links to the testing guide for optional ItemsAdder and MMOItems adapter contract tests.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to b3142

The README directs optional-test users to a guide with the complete JAR prerequisites, so the documented setup is complete and no merge-blocking concern remains.

• Autopilot · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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