transaction: Add support for using raw binary pointers conversation handler

This requires the allocating function to provide a binary pointer that
will be free'd by the conversation handlers finalizers.

This is for a more advanced usage scenario where the binary conversion
may be handled manually.

cmd/pam-moduler/tests/integration-tester-module/integration-tester-module_test.go

@@ -949,6 +949,10 @@ func Test_Moduler_IntegrationTesterModule(t *testing.T) {
 				if !pam.CheckPamHasBinaryProtocol() {
 					t.Skip("Binary protocol is not supported")
 				}
+			case pam.BinaryPointerConversationHandler:
+				if !pam.CheckPamHasBinaryProtocol() {
+					t.Skip("Binary protocol is not supported")
+				}
 			}
 
 			tx, err := pam.StartConfDir(name, tc.user, tc.credentials, ts.WorkDir())