Error: Token pool is exhausted

Sentry Issue: [SHIELDS-77](https://sentry.io/organizations/shields/issues/2837466428/?referrer=github_integration)

```
Error: Token pool is exhausted
File "/app/core/token-pooling/token-pool.js", line 268, in TokenPool._nextBatch
throw Error('Token pool is exhausted')
File "/app/core/token-pooling/token-pool.js", line 305, in TokenPool.next
token = this._nextBatch()
File "/app/services/librariesio/librariesio-api-provider.js", line 75, in LibrariesIoApiProvider.fetch
token = this.standardTokens.next()
File "/app/core/base-service/base.js", line 233, in LibrariesIoRepoDependencies._request
const { res, buffer } = await this._requestFetcher(url, options)
File "/app/core/base-service/base-json.js", line 45, in LibrariesIoRepoDependencies._requestJson
const { buffer } = await this._request({
...
(5 additional frame(s) were not displayed)
```

Read core/token-pooling/token-pool.js at TokenPool._nextBatch and next, then follow services/librariesio/librariesio-api-provider.js:75 into the request path in core/base-service/base.js and base-json.js. Reproduce or inspect the exhaustion path and verify that Libraries.io requests no longer raise this error with regression coverage.

Written by the indexing model from the issue text.