feat(ci): add Test PyPI release workflow for splunk-ao-a2a

[adityamehra]

Summary

Adds .github/workflows/release-splunk-ao-a2a-test.yaml — a pipeline that builds and publishes the splunk-ao-a2a package to Test PyPI.

How it works

• PR push: runs tests → publishes 0.1.0.dev<run_number> to Test PyPI (clean version stays reserved)
• workflow_dispatch with version: runs tests → publishes the exact version supplied
• workflow_dispatch without version: runs tests → publishes whatever is in pyproject.toml

Job chain

test → build → publish (each step gates the next)

Notes

• All action references pinned to commit SHA (matching ci-tests-splunk-ao-a2a.yaml pattern)
• Matches the pending Trusted Publisher on test.pypi.org (workflow: release-splunk-ao-a2a-test.yaml, environment: testpypi)
• Builds with python -m build (hatchling backend)

Made with Cursor

[adityamehra]

Applied the same changesets from PR #48 to this workflow:

Version input validation — Added a grep -Eq check in the Override version step (manual workflow_dispatch path) that rejects anything that is not an explicit PEP 440 version number. Bump keywords like patch, major, or minor will fail fast with a clear ::error:: message before touching any files. The PR-triggered .dev path is unaffected since it computes the version automatically from pyproject.toml. (SHA pinning was already in place from the initial commit.)