Update Go workflow to include libsecp256k1 for tests and bump version to v0.25.5

- Modified the CI workflow to copy the `libsecp256k1.so` file to the root directory for test accessibility.
- Enhanced the `InitPub` method in the `FallbackSigner` to parse the x-only public key for verification.
- Bumped version to v0.25.6 to reflect these updates.

pkg/interfaces/signer/p8k/p8k.go

@@ -362,6 +362,11 @@ func (s *FallbackSigner) InitPub(pub []byte) (err error) {
 	s.xonlyPub = make([]byte, 32)
 	copy(s.xonlyPub, pub)
 
+	// Parse the x-only public key into a full public key for verification
+	if s.pubKey, err = schnorr.ParsePubKey(pub); err != nil {
+		return errorf.E("failed to parse public key: %w", err)
+	}
+
 	return nil
 }