test: Add language-neutral protocol fixtures and Python runner (Phase 1)

[Titas-Ghosh]

Hi @pradeeban, as discussed in #440, here is the first PR to establish the protocol conformance infrastructure.

Summary

This PR introduces Phase 1 of the protocol conformance work in a strictly non-breaking, report only way.
It adds a language neutral fixture format and a Python conformance runner to establish an observable baseline for core protocol behavior, without changing any runtime logic.

Recent testing improvements added strong coverage, but we still lack a reusable conformance layer that can be extended across bindings in later phases. This PR lays the foundation by focusing purely on baseline infrastructure and Python verification.

Scope (Phase 1 only)

• Fixture Schema: Added tests/protocol_fixtures/schema.phase1.json
• Python Cases: Added initial fixture cases in tests/protocol_fixtures/python_phase1_cases.json
• Documentation: Added the protocol contract/docs in tests/protocol_fixtures/PROTOCOL_FIXTURES.md
• Test Runner: Added the Python conformance runner in tests/test_protocol_conformance.py

Safety / Non-Goals

• NO runtime behavior changes in concore.py, concoredocker.py, or any other runtime files.
• NO cross-language enforcement in this PR.
• NO CI gate tightening or failing builds in this PR.

Validation

Command Executed:

python -m pytest -v tests/test_protocol_conformance.py

Result:

• 7 tests passed (fixture schema + conformance cases for parse_params, initval, and write_zmq).

Evidence

1) Minimal PR Scope & Line Impact

2) Conformance Runner Passing

Next Phase (separate PR)

If you think this foundation is proper and can be merged , then the next steps that i will be working on are :

• Expand adapters/runners for other bindings in baseline mapping mode.
• Classify differences as required, implementation_defined, or known_deviation before any enforcement.

Happy to iterate based on your feedback!