* added async_download()
* add case tests for ExecutionEngine download() and async_download()
* change async_download() to download_async() in Engine class and subsequent tests
* fixed reactor import in test_engine.py
* Simplify TestEngineDownloadAsync.
* replaced tearDown by self.engine.downloader.close in test_engine.py and replace @defer.inlineCallbacks by @inlineCallbacks
* Simplify ExecutionEngine.download().
* Remove an unneeded import.
* Refactor ExecutionEngine.download{,_async}() tests.
* Deprecate ExecutionEngine.download().
* Update doc examples to use download_async().
* Replace uses of download() with download_async().
* Fix test_downloadermiddleware_robotstxt.py.
* Remove a stray file.
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Co-authored-by: Andrey Rakhmatullin <wrar@wrar.name>
* Migrate to pytest-twisted (WIP)
* Some typing fixes.
* Make --reactor=asyncio the default again.
* Try installing the correct event loop policy in tests on Windows.
* Make reactor_pytest a normal fixture.
* Fix test warnings.
* Fix FTPDownloadHandler teardown.
* Cleanups, typing.
* More cleanup.
* Update only_asyncio/only_not_asyncio mark messages.
* Switch to pytest.raises().
* Add matches= to broad pytest.raises().
* Adjust the test_nonserializable_object() regex for Python <= 3.11.
* Adjust the test_nonserializable_object() regex for PyPy.
* Adjust other test exception regexes for PyPy.
* Cleanup.
Make the robots.txt parser configurable through the new ROBOTSTXT_PARSER setting, support the Reppy and Robotexclusionrulesparser parsers, and allow implementing custom robots.txt parsers.