chore: batch account creation

[Nodonisko]

Explanation

This batches some calls during account creation after SRP import. It reduced time it took from ~35s to ~9s on my device for SRP with ~250 accounts.

I am not sure if this is worth merging because of https://github.com/MetaMask/core/pull/6654

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

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[!NOTE] Batches EVM account discovery/creation and debounces wallet/group syncs to cut redundant vault updates during large imports.

• MultichainAccountService:
  • Add debounced sync pipeline (50ms) using #pendingWalletSyncs and #pendingGroupSyncs; replace immediate wallet.sync()/group.sync() on account add with queued flush via #scheduleSync() and #flushSyncs().
• MultichainAccountWallet:
  • Optimize discovery: detect contiguous active EVM accounts, then batch-create them and skip sequential EVM discovery; update maxGroupIndex accordingly.
• EvmAccountProvider:
  • Add findActiveAccountCount (checks activity via eth_getTransactionCount), bulkCreateAccounts (single keyring write), and internal #createAccountsBatch helper; expose address/tx-count helpers for discovery flow.

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