Fix Misclassification of ECDSA Signatures in verifyMultisig()

[valentinfernandez1]

This PR addresses issue #1898 by refining the logic in verifyMultisig() to correctly distinguish between ECDSA, Ed25519, and Sr25519 signatures.

Problem:
Previously, verifyMultisig() misidentified certain ECDSA signatures (65 bytes) as Ed25519 or Sr25519 signatures (64 bytes) when the first byte of the ECDSA signature was 0 or 1. This happened because the function interpreted the first byte as a multisignature prefix rather than part of the ECDSA signature itself.

Solution:

• Improved signature length handling:

  • If the signature is 66 bytes, it is treated as an ECDSA signature prefixed with a crypto type byte, so the prefix is removed before verification.
  • If the signature is 65 bytes, it could be:
    • A proper ECDSA signature, which should remain unchanged for verification.
    • An Ed25519/Sr25519 signature (1-byte prefix + 64-byte signature), in which case the prefix is removed before verification.

• Improved verification order:

  • First, attempt Ed25519/Sr25519 verification by removing the prefix.
  • If verification fails, fall back to ECDSA verification using the full 65-byte signature.

  closes Signing and verifying a message using ECDSA sometimes fails #1898