Fetch the plugin catalogue and every plugin's releases, returning a handle.
fetch_callback is a JS async function (url: string) => Promise<Uint8Array>
used to fetch the manifests. All fetching happens here, up front; the
returned [PluginCatalog] then answers queries without further fetching.
Fetch the plugin catalogue and every plugin's releases, returning a handle.
fetch_callbackis a JS async function(url: string) => Promise<Uint8Array>used to fetch the manifests. All fetching happens here, up front; the returned [PluginCatalog] then answers queries without further fetching.