chore(oss): audit the server package and resync the SDK mirrors

Split the 657-line operation service into eor, submit, and verify
modules, add the AGENT_REVOKED and KEY_RETIRED codes the Backend already
emits, and condense every multi-line comment. Mirror Node, Python, and
Go at 2.1.0 with the deep-health 503, non-idempotent retry, rotation
grace, and path-encoding fixes. Document which routes and response
fields the self-hosted server does not provide.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

sdks/python/tests/test_pinned_directory.py

@@ -21,7 +21,7 @@ def test_darwin_private_directory_removal_uses_stdlib_dir_fd(
         calls.append((path, dir_fd))
 
     monkeypatch.setattr(_private_artifact.os, "rmdir", record_rmdir)
-    monkeypatch.setattr(_private_artifact.os, "supports_dir_fd", {record_rmdir})
+    monkeypatch.setattr(_private_artifact, "_RMDIR_SUPPORTS_DIR_FD", True)
 
     _private_artifact._remove_posix_private_directory(41, "private-container")