feat(sitemap): support root-level sitemap fallback for dynamic routes

[mateussilva92]

Fixes #18

Description

This PR enhances the Remix/React Router v7 sitemap generation by introducing a root handle fallback.

Previously, only route-level handle.sitemap functions were supported. Now:

• If a route defines a handle.sitemap, it will run for that route.
• If a route does not define a sitemap handle, the root.tsx sitemap function will run as a fallback if it exists.

This ensures consistent sitemap generation across all routes and reduces duplication for shared logic like multilingual alternates.

Type of change

Please mark relevant options with an x in the brackets.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Algorithm update - updates algorithm documentation/questions/answers etc.
• Other (please describe):

How Has This Been Tested?

This was tested locally directly on a React Router v7 project that I'm currently working on. I defined a handle function that returned a object with a sitemap function on my root.tsx and then checked the sitemap generated.

• Integration tests
• Unit tests
• Manual tests
• No tests required

Reviewer checklist

Mark everything that needs to be checked before merging the PR.

• Check if the UI is working as expected and is satisfactory
• Check if the code is well documented
• Check if the behavior is what is expected
• Check if the code is well tested
• Check if the code is readable and well formatted
• Additional checks (document below if any)

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