* Deprecate spider args of spider middleware methods.
* Deprecate the spider arg of pipeline process_item().
* Fix a typing issue.
* Deprecate the spider arg of pipeline {open,close}_spider().
* Cleanup.
* Update docs.
* Add pragma: no cover to some deprecated code.
* More tests.
* More tests.
* More tests.
* Simplify _process_parallel().
* Add a crawler argument to MiddlewareManager.__init__().
* Deprecate the spider argument in some MiddlewareManager subclasses.
* Remove the spider argument from ExecutionEngine.open_spider_async().
* Remove the spider argument from Scraper.open_spider().
* Fix the Scraper.close_spider() type hint.
* Remove the spider argument from Downloader internals.
* Deprecate the spider arg of download_func.
* Deprecate the spider arg of Downloader.fetch().
* Deprecate the spider arg of ItemPipelineManager.process_item().
* Fix pylint.
* Tests for MiddlewareManager spider code.
* Deprecated spider arg handling for custom pipeline managers.
* Add a test for the deprecated spider arg in a custom downloader.
* Remove TODO.
* Fix pylint.