the regex filters which the plugin's resolvers should use for the initial interception of resource-paths.
TODO: this might be error-prone, since my parsePackageUrl function requires the specifier to be "jsr:".
a better approach might be to use a specifiers field, similar to the npm-plugin's config.specifiers option.
but it does come with the downside that the specifier will always be entriely replaced with "jsr:".
specify which namespaces should be intercepted by the jsr-plugin.
all other namespaces will not be processed by this plugin.
if you have a plugin with a custom loader that works under some "custom-namespace",
you can include your "custom-namespace" here, so that if it performs a jsr-specifier import,
that import path will be captured by this plugin, and then consequently fetched by the http-loader plugin.
but do note that the namespace of the loaded resource will switch to the http-plugin's loader namespace
(which defaults to PLUGIN_NAMESPACE.LOADER_HTTP), instead of your "custom-namespace".
configuration options for the jsrPluginSetup and jsrPlugin functions.