docs: Improvements on provider_codegen for type hints and multi-line yaml descriptions (#4033)

# What does this PR do?

This PR improves type hint cleanup in auto-generated provider
documentation by adding regex logic.

**Issues Fixed:**
- Type hints with missing closing brackets (e.g., `list[str` instead of
`list[str]`)
- Types showing as `<class 'bool'>`, `<class 'str'>` instead of `bool`,
`str`
- The multi-line YAML frontmatter in index documentation files wasn't
ideal, so we now add the proper `|` character.

**Changes:**
1. Replaced string replacement (`.replace`) with regex-based type
cleaning to preserve the trailing bracket in case of `list` and `dict`.
2. Adds the `|` character for multi-line YAML descriptions.
3. I have regenerated the docs. However, let me know if that's not
needed.

## Test Plan

1. Ran uv run python scripts/provider_codegen.py - successfully
regenerated all docs
2. We can see that the updated docs handle correctly type hint cleanup
and multi-line yaml descriptions have now the `|` character.

### Note to the reviewer(s)

This is my first contribution to your lovely repo! Initially I was going
thourgh docs (wanted to use `remote::gemini` as provider) and realized
the issue. I've read the
[CONTRIBUTING.md](https://github.com/llamastack/llama-stack/blob/main/CONTRIBUTING.md)
and decided to open the PR. Let me know if there's anything I did wrong
and I'll update my PR!

---------

Signed-off-by: thepetk <thepetk@gmail.com>
Co-authored-by: Ashwin Bharambe <ashwin.bharambe@gmail.com>

docs/docs/providers/safety/index.mdx

@@ -1,7 +1,8 @@
 ---
-description: "Safety
+description: |
+  Safety
 
-    OpenAI-compatible Moderations API."
+      OpenAI-compatible Moderations API.
 sidebar_label: Safety
 title: Safety
 ---