Fix #2249: Use slice() instead of subarray() to preserve Buffer type

[R-Panic]

Fixes #2249

Summary

Fixed Buffer type mismatch issue in PSBT Taproot handling where Buffer.subarray() was returning Uint8Array instead of Buffer, causing Buffer.equals() comparisons to fail even when byte content is identical.

Changes

• Changed script.subarray(2, 34) to script.slice(2, 34) in getPrevoutTaprootKey()
• Changed signature.subarray(0, 64) to signature.slice(0, 64) in trimTaprootSig()

Root Cause

Node.js Buffer.subarray() returns a Uint8Array view of the underlying buffer, while Buffer.slice() returns a new Buffer with its own backing. The issue comment in #2249 explains:

Buffer.slice() --> returns a Buffer
Buffer.subarray() --> returns a Uint8Array

Impact

• Fixes spurious Buffer.equals() failures in BIP371 PSBT Taproot signature verification
• Ensures consistent type (Buffer) when comparing Taproot output keys
• No behavioral changes - both methods produce identical byte content

Testing

Manual verification: The fix matches the exact solution provided by the issue reporter and addresses both occurrences identified in the codebase.

[junderw]

We are migrating away from Buffer.

The solution is not to move back to Buffer, it's to fix the BIP371 code to not use Buffer.equals().

[junderw]

Oh, I see. The issue is from an old version.

The current version no longer has the same issue. If it does, let me know.