fix(i18n): pass search params to fallback

[mtwilliams-code]

Changes

• makes the i18n middleware when used for fallbacks pass on the search params to the subsequent render.
• closes issue i18n: fallbacks strip search params #12546

Testing

Tested locally with the same code in the stackblitz example in issue. Ran all i18n test suites. Did not add a specific test for this - if maintainers want I will, but wanted feedback on willingness to include this before I dove into the fixtures.

Docs

/cc @withastro/maintainers-docs for feedback!
May need docs. The current behavior is also undocumented and imo less intuitive.

[changeset-bot]

🦋 Changeset detected

Latest commit: 23a040f

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

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[github-actions]

This PR is blocked because it contains a minor changeset. A reviewer will merge this at the next release if approved.

[codspeed-hq]

CodSpeed Performance Report

Merging #12547 will degrade performances by 11.93%

_{Comparing mtwilliams-code:fix-i18n-search (23a040f) with main (65e50eb)}

Summary

⚡ 3 improvements
❌ 1 regressions
✅ 2 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	mtwilliams-code:fix-i18n-search	Change
❌	Rendering: streaming [false], .md file	21.2 ms	24.1 ms	-11.93%
⚡	Rendering: streaming [true], .astro file	1.8 s	1.4 s	+24.14%
⚡	Rendering: streaming [true], .md file	16.4 ms	12.8 ms	+27.86%
⚡	Rendering: streaming [true], .mdx file	1.2 s	1 s	+13.29%

[ascorbic]

This looks good. Could you add a test for this? Probably in packages/astro/test/i18n-routing.test.js