fix: reduce loop test igpconfig (#4005)

### Description
Refactor `testIgpConfig` in `testUtils.ts` for Enhanced Readability and
Maintainability by reduce loop
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What's included in this PR?
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### Drive-by changes
1. **Constant Usage:** Introduced `OVERHEAD_COST` as a constant to
replace the magic number `60000`, making the purpose of this value
clearer and the code easier to update.
2. **Improved Readability:** By using descriptive names and constants,
the function is now easier to understand at a glance, which is
particularly beneficial for new contributors or during code reviews.
3. **Dynamic Configuration Logic:** Ensured that the configuration for
`overhead` and `oracleConfig` is dynamically generated for each chain,
excluding the current chain to simulate realistic test scenarios.
<!--
Are there any minor or drive-by changes also included?
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These changes do not alter the logic but make the codebase cleaner and
more maintainable.
### Related issues

<!--
- Fixes #[issue number here]
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### Backward compatibility

<!--
Are these changes backward compatible? Are there any infrastructure
implications, e.g. changes that would prohibit deploying older commits
using this infra tooling?

Yes/No
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### Testing

<!--
What kind of testing have these changes undergone?

None/Manual/Unit Tests
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---------

Co-authored-by: tiendn <tiendn.works@gmail.com>

typescript/.changeset/pink-mirrors-sneeze.md

@@ -0,0 +1,5 @@
+---
+'@hyperlane-xyz/sdk': major
+---
+
+Refactor testIgpConfig function for clarity and maintainability

typescript/sdk/src/test/testUtils.ts

@@ -63,25 +63,30 @@ const TEST_ORACLE_CONFIG = {
   tokenExchangeRate: ethers.utils.parseUnits('1', 10),
 };
 
+const TEST_OVERHEAD_COST = 60000;
+
 export function testIgpConfig(
   chains: ChainName[],
   owner = nonZeroAddress,
 ): ChainMap<IgpConfig> {
   return Object.fromEntries(
-    chains.map((local) => [
-      local,
-      {
-        owner,
-        oracleKey: owner,
-        beneficiary: owner,
-        // TODO: these should be one map
-        overhead: Object.fromEntries(
-          exclude(local, chains).map((remote) => [remote, 60000]),
-        ),
-        oracleConfig: Object.fromEntries(
-          exclude(local, chains).map((remote) => [remote, TEST_ORACLE_CONFIG]),
-        ),
-      },
-    ]),
+    chains.map((local) => {
+      const overhead: IgpConfig['overhead'] = {};
+      const oracleConfig: IgpConfig['oracleConfig'] = {};
+      exclude(local, chains).map((remote: ChainName) => {
+        overhead[remote] = TEST_OVERHEAD_COST;
+        oracleConfig[remote] = TEST_ORACLE_CONFIG;
+      });
+      return [
+        local,
+        {
+          owner,
+          oracleKey: owner,
+          beneficiary: owner,
+          overhead,
+          oracleConfig,
+        },
+      ];
+    }),
   );
 }