test: trim tautological self-checks from participant spec-oracle suites

[Brad-Edwards]

Problem

A behavioural audit of the Python test suites — checking for the "assert against yourself / mock the thing under test" anti-pattern that affected a sibling project — found that two executable spec-oracle test files contained acceptance-direction tests that are tautological:

• implementations/python/tests/test_participant_semantics_invariant_oracle.py
• implementations/python/tests/test_participant_runtime_invariants.py

Both files re-encode a formal spec's invariants as test-local predicates with no production callers (confirmed: zero references under src/ or packages/). Several tests asserted that a co-authored fixture / Hypothesis generator — constructed to satisfy those same predicates — does in fact satisfy them. Those checks pass by construction, cannot catch a wrong implementation, and inflate the apparent coverage of participant-semantics / participant-runtime behaviour when no production code is exercised.

The rest of the audit was clean: real parser/validator/runtime/conformance/CLI/MCP code runs across the suite. This issue is scoped to the two oracle files.

Fix

• Remove the tautological acceptance-direction tests:
  • semantics oracle: the catalog self-check and both Hypothesis "generator output satisfies the predicates" tests, plus the now-dead generator strategy and its imports.
  • runtime oracle: the six bare *_accepts_generated_valid_traces tests.
• Keep the load-bearing tests: the spec to catalog drift guard, the per-invariant mutation/rejection differential tests, the *_accepts_supported_*_variants over-rejection guards, and the canonical positive control (now commented as such).
• Relabel both module docstrings to state plainly that these are spec self-consistency oracles, not tests of production code, and to point at the suites that cover runtime enforcement behaviourally (test_sem_211_* … test_sem_218_*, test_run_305/306/311_*).

Verification

• ruff check clean; affected suites pass (35 tests); full suite still collects (2523 tests).