Add ChatModels wrapper for Cloudflare Workers AI (#27645)

Thank you for contributing to LangChain!

- [x] **PR title**: "community: chat models wrapper for Cloudflare
Workers AI"


- [x] **PR message**:
- **Description:** Add chat models wrapper for Cloudflare Workers AI.
Enables Langgraph intergration via ChatModel for tool usage, agentic
usage.


- [x] **Add tests and docs**: If you're adding a new integration, please
include
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.


- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

Additional guidelines:
- Make sure optional dependencies are imported within a function.
- Please do not add dependencies to pyproject.toml files (even optional
ones) unless they are required for unit tests.
- Most PRs should not touch more than one package.
- Changes should be backwards compatible.
- If you are adding something to community, do not re-import it in
langchain.

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

---------

Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Chester Curme <chester.curme@gmail.com>

docs/scripts/check_templates.py

@@ -44,7 +44,7 @@ def _get_headers(doc_dir: str) -> Iterable[str]:
     for cell in nb["cells"]:
         if cell["cell_type"] == "markdown":
             for line in cell["source"]:
-                if not line.startswith("##") or "TODO" in line:
+                if not line.startswith("## ") or "TODO" in line:
                     continue
                 header = line.strip()
                 headers.append(header)