Python 3.14 runtime image omits _zstd, so compression.zstd cannot import

### Expected Behavior

The official Python 3.14 Azure Functions runtime should include CPython's _zstd extension so that the Python 3.14 standard-library import `from compression import zstd` succeeds. Python 3.14 is GA for Azure Functions, and CPython documents Zstandard 1.4.5 or later as the build dependency for this optional standard-library module.

### Actual Behavior

In the official `mcr.microsoft.com/azure-functions/python:4-python3.14` image, importing `compression.zstd` raises `ModuleNotFoundError: No module named '_zstd'`. CPython's recorded build state reports `MODULE__ZSTD_STATE=missing`. The final image contains `libzstd.so.1`, but the extension was not compiled when CPython was built, so adding the runtime library or installing the third-party `zstandard` package cannot restore the missing standard-library extension.

### Steps to Reproduce

1. Pull the current official image:

`docker pull --platform linux/amd64 mcr.microsoft.com/azure-functions/python:4-python3.14`

2. Run the standard-library import:

`docker run --platform linux/amd64 --rm mcr.microsoft.com/azure-functions/python:4-python3.14 python -c "from compression import zstd"`

3. Inspect CPython's recorded module build state:

`docker run --platform linux/amd64 --rm mcr.microsoft.com/azure-functions/python:4-python3.14 python -c "import sysconfig; print(sysconfig.get_config_var('MODULE__ZSTD_STATE'))"`

4. Observe the import failure and the `missing` build state.

### Relevant code being tried

```shell
docker run --platform linux/amd64 --rm mcr.microsoft.com/azure-functions/python:4-python3.14 python -c "from compression import zstd"

docker run --platform linux/amd64 --rm mcr.microsoft.com/azure-functions/python:4-python3.14 python -c "import sysconfig; print(sysconfig.get_config_var('MODULE__ZSTD_STATE'))"
```

### Relevant log output

```shell
Python 3.14.4

Traceback (most recent call last):
File "", line 1, in
from compression import zstd
File "/opt/python/3/lib/python3.14/compression/zstd/__init__.py", line 29, in
import _zstd
ModuleNotFoundError: No module named '_zstd'

MODULE__ZSTD_STATE: missing

Installed runtime library:
libzstd1:amd64 1.5.5+dfsg2-2build1.1
libzstd.so.1
```

### requirements.txt file

```shell
No third-party requirements are needed. The failure reproduces directly in the unmodified Azure Functions base image.
```

### Where are you facing this problem?

Production Environment (explain below)

### Function app name

_No response_

### Additional Information

Image tested: `mcr.microsoft.com/azure-functions/python:4-python3.14`

Image digest at the time of testing:
`sha256:2504f2b6dff243d671183e9dd6d607d1ae8f35e3536aa14965ffc3516749c1b8`

CPython build requirements document Zstandard >= 1.4.5 for `compression.zstd`:
https://docs.python.org/3.14/using/configure.html#requirements-for-optional-modules

Impact: libraries may select the Python 3.14 standard-library Zstandard implementation based on the interpreter version. For example, `starlette-compress` uses `compression.zstd` on Python >= 3.14, so its default Zstandard support fails under this image even though it works with Python distributions that include `_zstd`. Installing the third-party `zstandard` package does not fix that import path.

Current application workaround: probe `importlib.util.find_spec("_zstd")` and disable Zstandard, falling back to Brotli or Gzip. The durable fix is to make the Zstandard development dependency available when CPython is compiled for the official Python 3.14 Functions runtime.