docs: fix trim for rust,ignore blocks (#18239)

## Which issue does this PR close?

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Issue was raised as comment:
#17913 (comment)

## Rationale for this change

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in the issue then this section is not needed.
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On current website can see:

<img width="752" height="458" alt="image"
src="https://github.com/user-attachments/assets/7df06070-528f-432d-8a11-cf92f86f5f34"
/>

-
https://datafusion.apache.org/library-user-guide/upgrading.html#projectionexpr-changed-from-type-alias-to-struct

Source document:


https://github.com/apache/datafusion/blob/408e1e4e2c46d673a067e05f3e363a6f51e641c4/docs/source/library-user-guide/upgrading.md?plain=1#L204-L218

<img width="771" height="711" alt="image"
src="https://github.com/user-attachments/assets/9472b6b6-1a7e-42f3-a9ae-17d55adfb491"
/>


-https://datafusion.apache.org/library-user-guide/extending-operators.html#optimizing-logical-plan

Source document:


https://github.com/apache/datafusion/blob/408e1e4e2c46d673a067e05f3e363a6f51e641c4/docs/source/library-user-guide/extending-operators.md?plain=1#L32-L57

`,ignore` should also be trimmed out.

## What changes are included in this PR?

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PR.
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Fix regex used in trimming rust blocks to account for optional `ignore`.

## Are these changes tested?

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Tested locally:

<img width="791" height="441" alt="image"
src="https://github.com/user-attachments/assets/ff679228-812a-47d5-876e-6fc8fb552bed"
/>

<img width="762" height="681" alt="image"
src="https://github.com/user-attachments/assets/7c551441-3579-4f65-bf41-325ac81fcc76"
/>

Existing blocks (with only `rust` and not `rust,ignore`) unaffected,
e.g. in catalogs page:

<img width="764" height="543" alt="image"
src="https://github.com/user-attachments/assets/c18376d5-974c-4510-89e4-4c777c860ca0"
/>


## Are there any user-facing changes?

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updated before approving the PR.
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No, doc changes.

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change` label.
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Author: Jefffrey

docs/rustdoc_trim.py

@@ -19,7 +19,7 @@
 from sphinx.application import Sphinx
 
 # Regex pattern to match Rust code blocks in Markdown
-RUST_CODE_BLOCK_PATTERN = re.compile(r"```rust\s*(.*?)```", re.DOTALL)
+RUST_CODE_BLOCK_PATTERN = re.compile(r"```rust(?:,ignore)?\s*(.*?)```", re.DOTALL)
 
 
 def remove_hashtag_lines_in_rust_blocks(markdown_content):