refactor tx_template and init_graph fn to use Cow

- refactor tx_template struct and init_graph
to use Cow type
- update the chain test_tx_graph test to use the
updated tx_template struct and init_graph fn
- update the test_tx_graph_conflicts to use the
updated tx_template and init_graph fn

[Issue: 1754]

Author: tvpeter

crates/chain/tests/test_tx_graph.rs

@@ -18,6 +18,7 @@ use bitcoin::{
 };
 use core::iter;
 use rand::RngCore;
+use std::borrow::Cow;
 use std::sync::Arc;
 use std::vec;
 
@@ -1135,28 +1136,28 @@ fn call_map_anchors_with_non_deterministic_anchor() {
 
     let template = [
         TxTemplate {
-            tx_name: "tx1",
-            inputs: &[TxInTemplate::Bogus],
-            outputs: &[TxOutTemplate::new(10000, Some(1))],
-            anchors: &[block_id!(1, "A")],
+            tx_name: Cow::Borrowed("tx1"),
+            inputs: vec![TxInTemplate::Bogus],
+            outputs: vec![TxOutTemplate::new(10000, Some(1))],
+            anchors: vec![block_id!(1, "A")],
             last_seen: None,
         },
         TxTemplate {
-            tx_name: "tx2",
-            inputs: &[TxInTemplate::PrevTx("tx1", 0)],
-            outputs: &[TxOutTemplate::new(20000, Some(2))],
-            anchors: &[block_id!(2, "B")],
+            tx_name: Cow::Borrowed("tx2"),
+            inputs: vec![TxInTemplate::PrevTx(Cow::Borrowed("tx1"), 0)],
+            outputs: vec![TxOutTemplate::new(20000, Some(2))],
+            anchors: vec![block_id!(2, "B")],
             ..Default::default()
         },
         TxTemplate {
-            tx_name: "tx3",
-            inputs: &[TxInTemplate::PrevTx("tx2", 0)],
-            outputs: &[TxOutTemplate::new(30000, Some(3))],
-            anchors: &[block_id!(3, "C"), block_id!(4, "D")],
+            tx_name: Cow::Borrowed("tx3"),
+            inputs: vec![TxInTemplate::PrevTx(Cow::Borrowed("tx2"), 0)],
+            outputs: vec![TxOutTemplate::new(30000, Some(3))],
+            anchors: vec![block_id!(3, "C"), block_id!(4, "D")],
             ..Default::default()
         },
     ];
-    let (graph, _, _) = init_graph(&template);
+    let (graph, _, _) = init_graph(template);
     let new_graph = graph.clone().map_anchors(|a| NonDeterministicAnchor {
         anchor_block: a,
         // A non-deterministic value