add util for handling remix headers generally

[nichtsam]

It's a bit tedious to manually merge Remix headers since the process is mostly the same.
This PR adds a utility to streamline that process.

Related Discussion #809
More details on the utility: https://gist.github.com/nichtsam/bff3a0e58f7edfad3985e9322582f67f

Test Plan

• There are test cases for various functionalities.
• Test cases with real use cases ensure the utility remains practical.

Checklist

• Tests updated
• Docs updated

[nichtsam]

Just for the record, reason for switching to draft: privatenumber/tsx#627
This is affecting vite and causing imports behavior to differentiate between tsx and node.

[nichtsam]

Just for the record, reason for switching to draft: privatenumber/tsx#627 This is affecting vite and causing imports behavior to differentiate between tsx and node.

I switch to another ESM cache-control parser to avoid encountering this issue.

[kentcdodds]

I think React Router v7 (single fetch specifically) changes how headers work a fair bit so I don't think I'll be merging this since I want to get on RR7 soon. Sorry I didn't get to you on this sooner!

[nichtsam]

I think React Router v7 (single fetch specifically) changes how headers work a fair bit so I don't think I'll be merging this since I want to get on RR7 soon. Sorry I didn't get to you on this sooner!

That’s totally fine! I was also thinking that single fetch might impact things.
Just wanted to finish up the PR. No worries, and thanks for the update!