Upgrade to bdk 4.0

To achieve this we also:

- upgrade rust-bitcoin to 0.26
- upgrade bitcoin-harness to latest version (which also depends bitcoin 0.26)
- upgrade to latest edcsa-fun
- replace cross_curve_dleq proof with sigma_fun (to avoid an upgrade dance over there)

swap/tests/testutils/electrs.rs

@@ -137,6 +137,7 @@ impl IntoIterator for ElectrsArgs {
             Network::Testnet => args.push("--network=testnet".to_string()),
             Network::Regtest => args.push("--network=regtest".to_string()),
             Network::Bitcoin => {}
+            Network::Signet => panic!("signet not yet supported"),
         }
 
         args.push("-vvvvv".to_string());