Improve stream handling (#244)

* Improve stream management

* Check swap for existing lockup/refund tx

* Set broadcast capacity to 30

packages/flutter/lib/flutter_breez_liquid_bindings_generated.dart

@@ -678,7 +678,7 @@ final class wire_cst_receive_payment_response extends ffi.Struct {
 }
 
 final class wire_cst_send_payment_response extends ffi.Struct {
-  external ffi.Pointer<wire_cst_list_prim_u_8_strict> txid;
+  external wire_cst_payment payment;
 }
 
 const double LIQUID_CLAIM_TX_FEERATE_MSAT = 100.0;