async fetchPackageMetrics({ namespace, packageName }) {
    return this._requestJson({
      schema: packageMetricsSchema,
      url: `https://thunderstore.io/api/v1/package-metrics/${namespace}/${packageName}`,
    })
  }
Fetches package metrics from the Thunderstore API.

@param {object} pkg - Package specifier
@param {string} pkg.namespace - the package namespace
@param {string} pkg.packageName - the package name
@returns {Promise<object>} - Promise containing validated package metrics