fix: ipni indexer fetch errors are caught

[SgtPooki]

• getErrorMessage function to wrap original error and get valid string
• use errors in error messages returned to user
• wrap fetch to ipni indexer with try/catch to handle errors here so we can continue with retry.

Added test that was failing before the fixes.. now passing. Updated tests with new error message expectations

Fixes #236

[SgtPooki]

self review

[Copilot]

Pull Request Overview

This PR improves error handling for IPNI indexer operations by introducing proper fetch error catching and more informative error messages. The changes enable the system to gracefully handle and retry network errors when querying the IPNI indexer, rather than failing immediately.

Key changes:

• Added getErrorMessage utility function to safely extract error messages from unknown error types
• Wrapped IPNI indexer fetch calls in try-catch blocks to handle network errors and enable retries
• Enhanced error messages throughout to include underlying error details using the new utility

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/core/utils/errors.ts	New utility function to safely extract error messages from unknown error types
src/core/utils/validate-ipni-advertisement.ts	Added try-catch around fetch calls, improved error messages with detailed context, and handles non-ok responses
src/test/unit/validate-ipni-advertisement.test.ts	Updated test to verify retry behavior on fetch errors, updated expected error message format to include full context

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