fix: add transform tests, cache prep phase, update docs

[mkolasinski-splunk]

• Add sourcetypes parsing from transforms and generate field tests for parsed sourcetypes.
• Add parser caching (ParserCache) to props/transform parsing and test generation so pytest-xdist workers reuse the same metadata/test parameters instead of re-parsing/ regenerating per worker.
• Clarify documentation around requirement tests (transport overrides hit both ingestion metadata and search queries) and sample generation (distinguishing XML transport overrides vs. conf-driven ingestion/search settings, describing how sample_count behaves for requirement XML samples).
• Keep the flow of requirement-test ingestion/search transparent so authors know what configuration controls what part of the pipeline.

LLMs were used to generate part of the changes.

[srv-rr-github-token]

🎉 This PR is included in version 6.4.0 🎉

The release is available on GitHub release

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