feat(ramps): adds a controller method for fetching ramps tokens

[georgeweiler]

Explanation

Adds a getTokens method to the ramps-controller. Currently, tokens are fetched in the mobile app via useRampTokens, which duplicates API logic and doesn't persist data. The new method centralizes token fetching in the controller, caches results, and stores tokens in controller state for persistence. This aligns token fetching with other ramps data (countries, eligibility) and prepares for mobile app integration in a follow-up PR.

References

https://consensyssoftware.atlassian.net/browse/TRAM-3018

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

---

Note

Adds region/action-aware token fetching and persistence to align with other ramps data.

• New RampsService#getTokens(region, action) and types (RampsToken, TokensResponse), with response validation
• New RampsController#getTokens(region?, action='buy') using request cache (TTL/dedup), normalizes region, caches per [region, action], and updates state.tokens only when matching current userRegion
• Controller state expanded with tokens (persisted, exposed in metadata); setUserRegion/updateUserRegion now clear tokens on change and on eligibility fetch failures
• init() now fetches userRegion + eligibility, then getTokens('buy'); handles failures gracefully
• Messenger action RampsService:getTokens added and wired; comprehensive tests for caching, normalization, error handling, and state transitions; changelog updated

^{Written by Cursor Bugbot for commit 750f506. This will update automatically on new commits. Configure here.}