class Zeitwerk::Loader

@sig (bool) -> Zeitwerk::GemLoader

is private, client code can only rely on the interface.
This method returns a subclass of Zeitwerk::Loader, but the exact type

the same file, in the unlikely case the gem wants to be able to reload.
except that this method returns the same object in subsequent calls from

loader.push_dir(__dir__)
loader.inflector = Zeitwerk::GemInflector.new(__FILE__)
loader.tag = File.basename(__FILE__, ".rb")
loader = Zeitwerk::Loader.new

require "zeitwerk"

This is a shortcut for

def for_gem(warn_on_extra_files: true)
  called_from = caller_locations(1, 1).first.path
  Registry.loader_for_gem(called_from, namespace: Object, warn_on_extra_files: warn_on_extra_files)
end