Resolve Client.Python-003, -005, -009 code-review findings

Client.Python-003: stream_events_raw and query_active_alarms passed `timeout`
to the stub with no TypeError fallback, unlike _unary. Both now route through
a shared _open_stream helper that strips `timeout` on TypeError.

Client.Python-005: discover_hierarchy buffered the entire Galaxy hierarchy in
memory. Added GalaxyRepositoryClient.iter_hierarchy, a lazy async generator
yielding objects page-by-page; discover_hierarchy is now a thin wrapper that
preserves its list contract. README documents iter_hierarchy.

Client.Python-009: added regression coverage for previously untested paths —
write2/add_item2 request shape, the MAX_BULK_ITEMS boundary, the None-argument
TypeError guards, TLS ca_file reading, and the non-auth map_rpc_error fallthrough.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/python/README.md

@@ -131,6 +131,25 @@ The methods return native Python types (`bool`, `datetime | None`, and a
 into the hierarchy without learning the underlying stub class. The
 service requires the `metadata:read` scope on the API key.
 
+`discover_hierarchy` buffers every object (with its full attribute list)
+into a single in-memory `list`. For a large Galaxy use `iter_hierarchy`
+instead — it is an async generator that fetches one page at a time and
+yields objects as they arrive, so peak memory stays bounded by a single
+page rather than the whole hierarchy:
+
+```python
+async with await GalaxyRepositoryClient.connect(
+    endpoint="localhost:5000",
+    api_key="<gateway-api-key>",
+    plaintext=True,
+) as galaxy:
+    async for obj in galaxy.iter_hierarchy():
+        print(obj.tag_name, obj.contained_name)
+```
+
+Pages are fetched lazily: the next page is only requested once the
+caller has consumed every object from the current page.
+
 ### Watching deploy events
 
 `GalaxyRepositoryClient.watch_deploy_events` opens a server-streaming