fix(lattice): reuse cached credentials in offscreen keyring

[yilmazbahadir]

Description

• Address an MV3 regression where the offscreen Lattice keyring repeatedly prompted for credentials despite having them cached.
• Short-circuit _getCreds when eth-lattice-keyring already has credentials, improve error handling around chrome.runtime.sendMessage, and align the type declaration with the runtime behavior.

Changelog

CHANGELOG entry: Fixed the Lattice hardware wallet flow to reuse cached credentials instead of asking users to reconnect every time.

Related issues

Fixes: N/A

Manual testing steps

1. Connect a Lattice device and pair it with MetaMask in the extension.
2. Reopen the extension and initiate another signing action that uses the Lattice keyring.
3. Confirm the connector window is not re-opened and the cached credential flow proceeds without errors.

Screenshots/Recordings

Before

N/A

After

N/A

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable (existing test harnesses do not cover offscreen runtime APIs; manual validation described above)
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

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