feat: export metadata builder (#5117)

### Description

<!--
What's included in this PR?
-->

Export `BaseMetadaBuilder` from sdk

### Drive-by changes

<!--
Are there any minor or drive-by changes also included?
-->

No

### Related issues

<!--
- Fixes #[issue number here]
-->

### 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
-->

Yes

### Testing

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

None/Manual/Unit Tests
-->

.changeset/happy-steaks-approve.md

@@ -0,0 +1,5 @@
+---
+'@hyperlane-xyz/sdk': patch
+---
+
+export BaseMetadataBuilder

typescript/sdk/src/index.ts

@@ -166,6 +166,7 @@ export {
 } from './hook/types.js';
 export { DerivedIsmConfig, EvmIsmReader } from './ism/EvmIsmReader.js';
 export { HyperlaneIsmFactory } from './ism/HyperlaneIsmFactory.js';
+export { BaseMetadataBuilder } from './ism/metadata/builder.js';
 export { decodeIsmMetadata } from './ism/metadata/decode.js';
 export {
   buildAggregationIsmConfigs,