feat: swap limit approvals

[DanielSinclair]

What changed (plus any additional context for devs)

• Removed the assetNeedsUnlocking function and simplified the approval flow by directly using allowanceNeeded from the quote
• Changed token approvals from using MaxUint256 (unlimited) to using the exact amount needed for the transaction
• Updated the approvalAmount type in RainbowTransaction to accept any string value
• Removed redundant parameters from estimateUnlockAndSwap and estimateUnlockAndCrosschainSwap functions
• Simplified gas estimation logic for swaps by relying on the allowanceNeeded flag from quotes

Screen recordings / screenshots

N/A

What to test

• Token approvals should now use the exact amount needed instead of unlimited approvals
• Swaps should work correctly with the new approval flow
• Gas estimation for swaps should be accurate
• Cross-chain swaps should function properly with the new approval mechanism

[DanielSinclair]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: delegation developer settings #7016
• feat: delegation wallet management/preferences #7015
• feat: delegation revoke sheets, confirmations #7014
• feat: atomic swaps #6975
• refactor: transaction simulation uniformity #7019
• feat: swap limit approvals #7018 👈 (View in Graphite)
• chore: delegation sdk, service injection  #7017
• refactor: swap sdk type safety #6971 : 1 other dependent PR (#7002 )
• 7702

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