Create/Import: Enhancement - remove duplicate work and introducing controlled concurrency

[cmgustavo]

This PR improves app-side performance for createKey and serverAssistedImport by removing duplicate wallet creation and introducing controlled concurrency.

Onboarding

• Prevent delay (show the ongoingprocess) when pressing Create Key button during the Onboarding

createKey

• Added controlled concurrency when creating wallets (createMultipleWallets)
• Reduced strict sequential execution

import (serverAssistedImport)

• Removed duplicate wallet creation attempts in createWalletsForAccounts
• Implemented wallet-level deduplication (account + chain + coin)
• Avoided unnecessary createMultipleWallets calls for already existing wallets
• Eliminated bwc.ErrorCOPAYER_REGISTERED noise during import

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Results

createKey

• Before: ~36.6s
• After: ~20.7s
• Improvement: ~43.5% faster (~15.9s saved)

import

• Before: ~77.5s
• After: ~66.0s
• Improvement: ~11.5s faster