Port 6 missing StreamingPlan option tests to test_thread_faithful.py

[patrick-chinchill]

Test gap — StreamingPlan option variants untested.

What's missing

Upstream `thread.test.ts` has a `[Streaming]` block with 6 tests that exercise the `StreamingPlan` options surface (`groupTasks`, `endWith`, `updateIntervalMs`, etc.):

```
[Streaming] should pass StreamingPlan PostableObject options to adapter.stream
[Streaming] should pass StreamingPlan with only groupTasks
[Streaming] should pass StreamingPlan with only endWith
[Streaming] should pass StreamingPlan with only updateIntervalMs
[Streaming] should route StreamingPlan through fallback when adapter has no native streaming
[Streaming] should still work without options (backward compat)
```

Python's `test_thread_faithful.py` doesn't translate these. Need to verify the options are actually wired through to adapter streaming calls and not dropped.

Risk

If `thread.stream(plan, options)` drops `updateIntervalMs` or `endWith` somewhere in the Python port, nobody would know until a consumer noticed throttling or a missing end-card in production.

Fix

1. Verify `StreamingPlan` options are passed to adapter `stream(...)` calls (and to the fallback-streaming path).
2. Translate the 6 tests line-by-line from `thread.test.ts`.
3. Run `verify_test_fidelity.py` to confirm 0 missing under `[Streaming]`.

Acceptance

• `StreamingPlan` options (groupTasks, endWith, updateIntervalMs) propagate through to adapter streaming
• Fallback path also honors the options
• 6 faithful tests translated from `thread.test.ts`