refactor: make storage-wrapper operations synchronous

What is this about?

Now that we use MMKV, device storage operations are synchronous.

Our storage-wrapper methods are async only to support E2E, causing the whole storage-wrapper class to be behind a promise based architecture.

We need to decouple E2E fallbacks from the storage-wrapper implementation to have properly typed mmkv operations.

Scenario

N/A

Design

N/A

Technical Details

PR feat: Enable feature Flag Values with Scope Based on "threshold" in mobile has a draft commit on how it expects storage-wrapper interface to be.

Threat Modeling Framework

N/A

Acceptance Criteria

storage-wrapper methods to be sync when not running on E2E mode

Stakeholder review needed before the work gets merged

• Engineering (needed in most cases)
• Design
• Product
• QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
• Security
• Legal
• Marketing
• Management (please specify)
• Other (please specify)

References

Epic: https://github.com/MetaMask/metamask-mobile/issues/10784

Start by reviewing the storage-wrapper implementation and the draft commit f43d4e848843572f1c08b8f7aa29d15dab0d924e referenced in the issue. Trace how E2E fallbacks are connected, then verify that storage-wrapper methods are synchronous outside E2E mode and that the required automation tests pass.