fix(assets-controllers): parallelize chain processing in token detection

[vinnyhoward]

Explanation

Current State

The TokenDetectionController#detectTokensUsingRpc method processes blockchain networks sequentially using a for...await loop. When multiple networks are enabled (e.g., 20 networks in MetaMask Mobile), each chain must complete token detection before the next chain can start. This creates a severe performance bottleneck:

• 20 healthy networks (2s each): 40 seconds total
• 20 networks with 1 slow RPC (30s timeout): 68 seconds total
• 20 networks with multiple slow RPCs: 100+ seconds

This makes the app feel frozen and causes users to think it has crashed.

Solution

This PR refactors #detectTokensUsingRpc to execute all chains in parallel:

1. Replace sequential loop: Changed from for...await loop to Promise.allSettled() with parallel execution
2. Improve error isolation: Use allSettled instead of all so one failing chain doesn't block successful ones
3. Maintain per-chain logic: Token detection within each chain remains unchanged (already parallelized)

Performance Impact

• 20× faster with multiple networks (100s → 5s)
• Tokens from fast networks appear immediately
• Slow/failed chains don't block the entire detection process
• Better user experience: progressive token display instead of long freeze

Implementation Details

The change follows the same pattern already used successfully in:

• TokenRatesController.ts:436
• CurrencyRateController.ts:255

References

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