fix(deps): declare httpx, unbreaking partial-install (torch) for every PR (#2547)

## Summary

`partial-install (torch)` has been failing on **every** PR since
2026-09-24 — including PRs whose branches predate the breakage — and
because it is a *collection* error rather than a test failure, it aborts
the entire run:

```
ImportError while importing test module '.../tests/unit/torch/speculative/plugins/test_hf_streaming_dataset.py'
E   ModuleNotFoundError: No module named 'httpx'
collected 2243 items / 1 error / 45 skipped
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
```

`unit-pr-required-check` aggregates it, so nothing currently merges on a
fresh run.

## What happened

**No code changed.**
`modelopt/torch/speculative/plugins/hf_streaming_dataset.py` has
imported `httpx` at module scope since #1509 (2026-06-02), and `httpx`
has never appeared in `pyproject.toml`. It arrived only transitively:
`dev-test` → `timm` → `huggingface_hub` → `httpx`.

**huggingface_hub 2.0.0**, published **2026-09-24T12:01:21Z**, replaced
`httpx<1,>=0.23.0` with the separate **`httpx2<3,>=2.0.0`**
distribution. Different package name, so `httpx` stopped being installed
and the chain disappeared.

The boundary is exact — every run *created* before that timestamp
passes, every one after fails:

| PR | run created | result |
|---|---|---|
| #2536 / #2535 | 09-23 22:02 | pass |
| #2500 | 09-23 23:45 | pass — **merged 09-24 20:01 on this stale-green
result** |
| *hub 1.33.0 (still requires httpx)* | *09-24 09:49* | |
| **hub 2.0.0 published** | **09-24 12:01** | ← |
| #2539 | 09-24 16:57 | fail |
| #2544 | 09-24 18:32 | fail |
| #2216 | 09-25 11:58 | fail |

#2500 merging afterwards is not a counterexample: GitHub does not re-run
checks at merge time, so it merged on a result from ~20 hours earlier.
That is also why this went unnoticed.

## The changes

### 1. Declare `httpx` in the `hf` extra

`httpx` is not incidental to streaming — it is the only transport:

- every fetch is HTTP: `POST /v1/completions` to the vLLM serve plus
`GET /meta` and `/desc` against the connector's sidecar, all through
`httpx.Client`;
- there is no non-HTTP path — the base `StreamingDataset._fetch` is an
abstract seam and `EagleVllmStreamingDataset._fetch` is its only
implementation;
- no other HTTP library appears in the module (`requests` / `urllib` /
`aiohttp`: zero hits, and `requests` is not declared either);
- even the retry predicate is built from it: `_TRANSIENT_FETCH_ERRORS =
(httpx.HTTPError, OSError)`.

It belongs in `hf` rather than in the core `dependencies`: the same
module needs `transformers.trainer_pt_utils` at module scope, so one
extra already gates the whole file, and a core install has no use for an
HTTP client. The bound matches the 0.x API the code uses — `httpx` has
no 1.0 release, and 2.x is a different distribution.

This is the part that stops it recurring. `[hf]` currently gets `httpx`
only because `datasets` happens to require it — the same accident with a
different supplier, one release away from repeating.

### 2. Acquire `httpx` in the test through the existing skip guard

The test file already intends to skip where the extra is absent — it has
`pytest.importorskip("transformers")` and a comment explaining why, and
`transformers` is absent in this job too. It broke only because `import
httpx` sat **five lines above** that guard, where a missing module ends
collection instead of skipping one file.

## Verification

- With everything installed: **18 passed**, no behaviour change.
- The import-order property is checked with an AST walk over the
module's top-level statements: no `hf`-extra-only import precedes the
first `importorskip` (which is now line 41).
- A faithful local reproduction was attempted and abandoned honestly:
hiding `httpx` locally also breaks `huggingface_hub` 1.28, which
`modelopt.torch.opt.plugins.huggingface` imports, so the local failure
is not the CI one. CI is the oracle for that half — this PR's own
`partial-install (torch)` run is the check that matters.

## Scope

Two files, five lines of declaration and four of test import order.
Deliberately not folded into any feature PR: it blocks the whole repo,
and burying a repo-wide fix inside unrelated work is how these stay
invisible.

🤖 Generated with [Claude Code](https://claude.com/claude-code)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Optional Hugging Face installations now include `httpx`, supporting
features that require HTTP communication without requiring it for all
installations.
* **Tests**
* Hugging Face streaming dataset tests now skip when `httpx` is
unavailable, allowing the remaining test suite to be collected and run
without it.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: h-guo18 <67671475+h-guo18@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: h-guo18

pyproject.toml

@@ -82,6 +82,7 @@ hf = [
     "datasets>=3.0.0",
     "deepspeed>=0.9.6; platform_system != 'Darwin' and platform_system != 'Windows'",
     "diffusers>=0.32.2",
+    "httpx>=0.23.0,<1",
     "huggingface_hub>=0.24.0",
     "nltk",
     "peft>=0.17.0",

tests/unit/torch/speculative/plugins/test_hf_streaming_dataset.py

@@ -30,12 +30,12 @@
 import types
 from unittest.mock import MagicMock
 
-import httpx
 import pytest
 import torch
 
 # hf_streaming_dataset imports LabelSmoother at module scope.
 pytest.importorskip("transformers")
+httpx = pytest.importorskip("httpx")
 
 from modelopt.torch.speculative.plugins import hf_streaming_dataset
 from modelopt.torch.speculative.plugins.hf_streaming_dataset import (