test(python): cover body-or-no-content responses

[Copilot]

Adds Python SDK mock API coverage for Spector operations that return either a 200 model body or 204 no-content success response.

• Mock API coverage
  • Add shared sync and async tests for response/body-or-no-content.
  • Validate body deserialization, None for 204, raw status codes, and x-ms-request-id headers.

body, response = client.get_no_content(cls=lambda x, y, z: (y, x))

assert body is None
assert response.http_response.status_code == 204

• Spector dependency

  • Update @typespec/http-specs to the prerelease containing the scenario.

• Changelog

  • Add an internal entry for @typespec/http-client-python.

• Fixes [python] add test case for https://github.com/microsoft/typespec/pull/11677 #11721

[azure-pipelines]

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