Fix remarkMdxish performance issue on huge sites

[hippotastic]

Changes

• Fixes an issue reported by JamesScheller in our Discord support channel that causes a Maximum call stack size exceeded error when building sites with hundreds of Markdown pages.
• Background: The makeFromMarkdownLessStrict fix introduced in beta 41 was applied once per page render, inadvertently wrapping the extension function in multiple layers of fix functions. This caused the call stack to grow indefinitely.
• This PR changes this behavior by preparing all extensions (including the fix) just once and then reusing the prepared extensions later.

Testing

• Ran all tests.
• Successfully built the private example repo provided by the original issue reporter.

Docs

• Not a visible change, just a bugfix.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8dbfd5e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/markdown-remark	Patch

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[hippotastic]

@natemoo-re PTAL :) This is a fix for an unwanted side effect caused by a previous fix. 😅

[natemoo-re]

Thanks @hippotastic!