CSHLD-886: Fix incorrect hashbytes padding in sBTC withdraw builder

[abhi-bitgo]

Summary

Remove incorrect 32-byte zero-padding of BTC address hash bytes in the sBTC withdraw builder. P2PKH, P2SH, and P2WPKH addresses have 20-byte hashes and were being incorrectly padded to 32 bytes.

Linear: CSHLD-886

Changes

• Remove HASHBYTES_BUFFER_LENGTH constant and 32-byte zero-padding logic from withdrawParamsToFunctionArgs in sbtcWithdrawBuilder.ts
• Pass decoded.hashBytes directly to bufferCV instead of padding
• Add unit test assertions verifying correct hashbyte buffer lengths:
  • 20 bytes for P2PKH, P2SH, P2WPKH
  • 32 bytes for P2WSH, P2TR

Test Plan

• Unit tests added to verify hashbyte buffer lengths for each address type (P2PKH, P2SH, P2WPKH, P2WSH, P2TR)

[linear-code]

CSHLD-886