feat: isolate manual verification RPC usage

- add rpc node purpose support for general/manual_verify/both
- keep scan, WSS and health checks away from manual_verify nodes
- fallback manual hash verification from general RPC to manual_verify RPC
- add public cashier hash submission path and errno responses
- update tests for RPC selection, failover and manual payment flows

src/model/dao/mdb_table_init_test.go

@@ -0,0 +1,43 @@
+package dao
+
+import (
+	"testing"
+
+	"github.com/GMWalletApp/epusdt/model/mdb"
+)
+
+func TestDefaultRpcNodesIncludesManualVerifyEpusdtEvmNodes(t *testing.T) {
+	want := map[string]string{
+		mdb.NetworkEthereum: "https://rpc.epusdt.com/ethereum",
+		mdb.NetworkBsc:      "https://rpc.epusdt.com/binance",
+		mdb.NetworkPolygon:  "https://rpc.epusdt.com/polygon",
+	}
+	got := make(map[string]mdb.RpcNode)
+	for _, node := range defaultRpcNodes() {
+		if node.Purpose != mdb.RpcNodePurposeManualVerify {
+			continue
+		}
+		if _, ok := want[node.Network]; ok {
+			got[node.Network] = node
+		}
+	}
+
+	for network, url := range want {
+		node, ok := got[network]
+		if !ok {
+			t.Fatalf("missing manual_verify seed rpc node for %s", network)
+		}
+		if node.Url != url {
+			t.Fatalf("%s manual_verify seed url = %q, want %q", network, node.Url, url)
+		}
+		if node.Type != mdb.RpcNodeTypeHttp {
+			t.Fatalf("%s manual_verify seed type = %q, want %q", network, node.Type, mdb.RpcNodeTypeHttp)
+		}
+		if !node.Enabled {
+			t.Fatalf("%s manual_verify seed enabled = false, want true", network)
+		}
+		if node.Status != mdb.RpcNodeStatusUnknown {
+			t.Fatalf("%s manual_verify seed status = %q, want %q", network, node.Status, mdb.RpcNodeStatusUnknown)
+		}
+	}
+}