[python] Add mock_api coverage for single-discriminator no-subtypes scenario

[Copilot]

This adds python mock API coverage for the new Spector scenario introduced by the cross-language spec updates: a discriminated model with no declared subtypes. The PR extends existing single-discriminator tests in both sync and async suites and aligns local spec inputs to a version that contains the scenario.

• Test coverage: single-discriminator no-subtypes (shared sync/async)

  • Extended existing shared tests to cover:
    • get_no_subtypes_model()
    • put_no_subtypes_model(...)
  • Added Fish model assertions to validate the expected wire payload shape (kind, size).

• Spec dependency update for scenario availability

  • Updated @typespec/http-specs in packages/http-client-python/package.json (and lockfile) to a version containing the new scenario definitions used by regeneration.

• Change tracking

  • Added a Chronus internal entry for @typespec/http-client-python.

def test_get_no_subtypes_model(client):
    assert client.get_no_subtypes_model() == Fish(kind="salmon", size=10)

def test_put_no_subtypes_model(client):
    client.put_no_subtypes_model(Fish(kind="salmon", size=10))