Add EnokiClientError to expose enoki service error details (MystenLab…

…s#16362)

## Description 

Describe the changes or additions included in this PR.

## Test Plan 

How did you test the new or updated feature?

---
If your changes are not user-facing and do not break anything, you can
skip the following section. Otherwise, please briefly describe what has
changed under the Release Notes section.

### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

.changeset/plenty-cobras-matter.md

@@ -0,0 +1,5 @@
+---
+'@mysten/enoki': patch
+---
+
+Add EnokiClientError to expose error details

sdk/enoki/src/EnokiClient/index.ts

@@ -27,6 +27,28 @@ export interface EnokiClientConfig {
 	apiUrl?: string;
 }
 
+export class EnokiClientError extends Error {
+	errors: { code: string; message: string; data: unknown }[] = [];
+
+	constructor(status: number, response: string) {
+		let errors;
+		try {
+			const parsedResponse = JSON.parse(response) as {
+				errors: { code: string; message: string; data: unknown }[];
+			};
+			errors = parsedResponse.errors;
+		} catch (e) {
+			// Ignore
+		}
+		const cause = errors?.[0] ? new Error(errors[0].message) : undefined;
+		super(`Request to Enoki API failed (status: ${status})`, {
+			cause,
+		});
+		this.errors = errors ?? [];
+		this.name = 'EnokiClientError';
+	}
+}
+
 /**
  * A low-level client for interacting with the Enoki API.
  */
@@ -119,7 +141,7 @@ export class EnokiClient {
 		});
 
 		if (!res.ok) {
-			throw new Error('Failed to fetch');
+			throw new EnokiClientError(res.status, await res.text());
 		}
 
 		const { data } = await res.json();