fix(signing): use .toCompactRawBytes() for SECP256K1 signatures

[amathxbt]

Bug

secp256k1.sign() in @noble/curves v2 returns a Signature object, not a Uint8Array. The original code cast it as unknown as Uint8Array and passed the object directly to bytesToHex.

bytesToHex iterates bytes of whatever it receives; operating on a JavaScript object instead of typed bytes produces garbage hex for every SECP256K1 and ETHSECP256K1 signature generated by this SDK.

Impact: All transactions signed with SECP256K1 or ETHSECP256K1 keys are rejected by the network — the signature bytes are wrong.

Fix

Call .toCompactRawBytes() on the returned Signature object to obtain the correct 64-byte compact (r, s) representation before encoding.

// Before
return bytesToHex(secp256k1.sign(messageBytes, privKeyBytes) as unknown as Uint8Array);

// After
return bytesToHex(secp256k1.sign(messageBytes, privKeyBytes).toCompactRawBytes());

This matches how @noble/curves is documented and used for ed25519 (which already calls .sign() and gets a Uint8Array directly — ed25519 returns bytes, secp256k1 does not).