fix: unnecessary fee buffers

[meeh0w]

Summary

Jira ticket: no ticket
Figma: n/a

Notes

• Removes no-longer-necessary buffer being applied to Solana -> EVM cross-chain swaps
• Removes no-longer-necessary buffer being applied to the network fee (+10% for Bitcoin remains)

Testing

• Verify the reported fees for SOL -> ETH match Core Web

Media

n/a

[Copilot]

Pull request overview

This PR removes additional fee “buffers” previously applied in the Fusion (swap) flow, relying instead on the Fusion SDK’s native fee margin (feeUnitsMarginBps) while keeping the explicit 10% Bitcoin buffer.

Changes:

• Removed the Solana → EVM native fee multiplier logic (and the associated helper/constant).
• Removed the extra non-Bitcoin network-fee buffer in required token amount calculations (Bitcoin +10% remains).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
apps/next/src/pages/Fusion/lib/isSolanaToEvm.ts	Removed Solana→EVM quote detection helper (no longer needed after multiplier removal).
apps/next/src/pages/Fusion/fusion-config.ts	Removed the Solana→EVM native fee multiplier constant.
apps/next/src/pages/Fusion/contexts/hooks/useRequiredTokenAmounts.ts	Set non-Bitcoin network-fee buffer to 0 (keeps Bitcoin at 10%).
apps/next/src/pages/Fusion/contexts/hooks/useNativeFeeEstimate.ts	Removed Solana→EVM-specific fee buffering; now returns SDK totalFee directly.

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