refactor: Rename the HTTPX extra and clients to httpx2 - #1048

Updates the development lockfile to the current releases of our own
dependencies, and fixes the docs shortcut generator that the new client
broke.

- `apify-client` 3.1.3 -> 3.2.0
- `crawlee` 1.9.3 -> 1.10.0, which pulls `impit` 0.13.2 -> 0.14.0
- `website/generate_module_shortcuts.py` now skips attributes that raise
`ImportError` because an optional extra is missing. `apify-client`
renamed its HTTPX extra to `httpx2` and guards the import
(apify/apify-client-python#1048), so `inspect.getmembers` walking
`apify_client.http_clients` raised `ImportError` and broke the docs
build.

`pyproject.toml` constraints are untouched - both new versions already
satisfy them, so this only moves the lockfile used for development and
CI.

*✍️ Drafted by Claude Code*

`_httpx2.py` pulled the library in as `import httpx2 as httpx`, so the
module and its tests read
`httpx.*` throughout while the installed package is `httpx2`. Dropping
the alias lets the code name
the library it actually uses.

The rename follows through: the private transport attributes become
`_httpx2_client` and
`_httpx2_async_client`, matching the sibling adapter's `_impit_client` /
`_impit_async_client`, and
21 test functions plus the `UNSET_HTTPX2_TIMEOUT` constant lose the old
spelling. All of it is
private, so no public name moves. A search for the original `httpx`
under `src/` and `tests/` now
turns up only the two sentences that describe the library's lineage on
purpose.

It also cleans up link labels left over from #1048. Eight places wrote
`[HTTPX](https://github.com/pydantic/httpx2)`, giving the current client
the old library's name, and
the surrounding prose had the same split: docstrings said HTTPX while
the link beside them said
HTTPX2. The library calls itself HTTPX2, so 66 prose references now use
that name. The v2 upgrade
guide is the reverse case: it describes moving off the original `httpx`,
so its link goes back to
python-httpx.org, matching what the 2.5 docs already say. These changes
land in `docs/` only, so
they reach the docs site at `/next` until the next version snapshot.

No behavior changes. The 241 unit tests covering the HTTP clients,
headers, timeouts, and the
pluggable client still pass, 21 of them under new names.

*✍️ Drafted by Claude Code*