async calls to getLanguage to support nextjs 15

[tconroy]

Relates to issue: opral/inlang-paraglide-js#245

Starting with latest RC of Next.js 15 (RC 2), the request APIs (including headers()) is async: nextjs.org/blog/next-15-rc2#async-request-apis-breaking-change.

This change breaks the getLanguage() function from @inlang/paraglide-next, (on the server):

opral/monorepo@a0aaf62/inlang/source-code/paraglide/paraglide-next/src/app/getLanguage.server.ts#L14

This PR updates the getLanguage() function (every function that uses it) to be async.

Note: I was not actually able to test this locally in-repo, as I don't have Doppler access and couldn't get the local env running fully. However I did run unit tests and build, both of which appeared to be passing.

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[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[tconroy]

I have read the CLA Document and I hereby sign the CLA

[tconroy]

recheck

[asterikx]

@tconroy I think, it's best to mirror the new (async) function signatures in the client files (getLanguage.client.ts, initializeLanguage.client.ts, and createI18n.client.ts) to have an isomorphic API (same API on server & client). Otherwise, your changes look similar to mine overall. Thanks! 🙂

[samuelstroschein]

Good to merge and release with the minor request to change the client types to be sync.

[samuelstroschein]

@tconroy @asterikx to get this PR merged and released, i would go ahead and change the client function types to be sync again #3188 (comment). if nobody objects, I'll do the change tmr and get this PR published :)

[tconroy]

Sounds good. I've reverted that commit and have also merged in latest master to this branch, so should be all set.

[samuelstroschein]

Published as v0.7. Thanks @tconroy for the PR!