Update dependencies and refactor conversation key generation

- Added `github.com/ebitengine/purego` as a direct dependency to the project.
- Removed the unused `p8k.mleku.dev` dependency from the `go.mod` file.
- Refactored the `GenerateConversationKeyFromHex` function to clarify parameter order, aligning with the NIP-44 specification.
- Enhanced test cases for conversation key generation to ensure proper handling of public key formats and improved error messages.
- Updated the `Signer` interface to include methods for extracting and serializing public keys in compressed format.

pkg/crypto/p8k/schnorr.go

@@ -47,6 +47,23 @@ func (c *Context) KeypairXOnlyPub(keypair Keypair) (xonly XOnlyPublicKey, pkPari
 	return
 }
 
+// KeypairPub extracts the full public key (64-byte internal format) from a keypair
+func (c *Context) KeypairPub(keypair Keypair) (pubkey []byte, err error) {
+	if keypairPub == nil {
+		err = fmt.Errorf("keypair_pub function not available")
+		return
+	}
+
+	pubkey = make([]byte, PublicKeySize)
+	ret := keypairPub(c.ctx, &pubkey[0], &keypair[0])
+	if ret != 1 {
+		err = fmt.Errorf("failed to extract public key from keypair")
+		return
+	}
+
+	return
+}
+
 // SchnorrSign creates a Schnorr signature (BIP-340)
 func (c *Context) SchnorrSign(msg32 []byte, keypair Keypair, auxRand32 []byte) (sig []byte, err error) {
 	if schnorrsigSign32 == nil {

pkg/crypto/p8k/secp.go

@@ -67,6 +67,7 @@ var (
 	xonlyPubkeyParse     func(ctx uintptr, pubkey *byte, input32 *byte) int32
 	xonlyPubkeySerialize func(ctx uintptr, output32 *byte, pubkey *byte) int32
 	keypairXonlyPub      func(ctx uintptr, pubkey *byte, pkParity *int32, keypair *byte) int32
+	keypairPub           func(ctx uintptr, pubkey *byte, keypair *byte) int32
 
 	// ECDH functions
 	ecdh func(ctx uintptr, output *byte, pubkey *byte, seckey *byte, hashfp uintptr, data uintptr) int32
@@ -193,6 +194,7 @@ func registerSymbols() (err error) {
 	tryRegister(&xonlyPubkeyParse, "secp256k1_xonly_pubkey_parse")
 	tryRegister(&xonlyPubkeySerialize, "secp256k1_xonly_pubkey_serialize")
 	tryRegister(&keypairXonlyPub, "secp256k1_keypair_xonly_pub")
+	tryRegister(&keypairPub, "secp256k1_keypair_pub")
 	tryRegister(&xonlyPubkeyFromPubkey, "secp256k1_xonly_pubkey_from_pubkey")
 
 	// ECDH module
@@ -308,6 +310,11 @@ func (c *Context) SerializePublicKey(pubkey []byte, compressed bool) (output []b
 	return
 }
 
+// SerializePublicKeyCompressed serializes a public key in compressed format (33 bytes)
+func (c *Context) SerializePublicKeyCompressed(pubkey []byte) (output []byte, err error) {
+	return c.SerializePublicKey(pubkey, true)
+}
+
 // ParsePublicKey parses a serialized public key
 func (c *Context) ParsePublicKey(input []byte) (pubkey []byte, err error) {
 	pubkey = make([]byte, PublicKeySize)