feat(ramps): surface transak errors for the consumer to read

[georgeweiler]

Explanation

Adds throwTransakApiError util which will better handle error surfacing so that consumers can display errors to the user related to their Transak user account.

References

Related mobile PR: MetaMask/metamask-mobile#26296

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Scoped to error handling and test updates; behavior changes are limited to the shape/detail of thrown errors on failed Transak requests.

Overview
Surfaces richer Transak API failures by centralizing error handling into #throwTransakApiError, which reads the response body and (when possible) extracts Transak’s error.code into a thrown TransakApiError.

All Transak HTTP helpers (#transakGet/#transakPost/#transakPatch/#transakDelete) now use this unified error path instead of generic HttpError in some cases, and tests were added/updated to assert errorCode parsing and behavior when the error body isn’t JSON. Changelog updated to note improved TransakService error handling.

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[georgeweiler]

@metamaskbot release-preview