[feat]: Add support to external downloader aria2p (#31500)

[feat]: Add support to external downloader aria2p (#31500)

* feat: add class Aria2pFD

* feat: create call_downloader function

* feat: a colorful download interface to aria2pFD

* feat: change value name

* Apply suggestions from code review

Co-authored-by: dirkf <fieldhouse@gmx.net>
* Typo in suggestion

* fix: remove unused value

* fix: add not function to return value(0 is normal); add total_seconds to download.eta(timedelta object); add waiting status when hook progress

* fix: remove unuse method ..utils.format_bytes

* fix: be up to flake8

* fix: be up to flake8

* Apply suggestions from code review

* [feat] test external downloader aria2p

* [feat] test external downloader aria2p

* [fix] test_external_downloader.py

* Apply suggestions from code review

Co-authored-by: dirkf <fieldhouse@gmx.net>
* Apply suggestions from code review

Co-authored-by: dirkf <fieldhouse@gmx.net>
* Update test/test_external_downloader.py

Co-authored-by: dirkf <fieldhouse@gmx.net>
* Update test/test_external_downloader.py

Co-authored-by: dirkf <fieldhouse@gmx.net>
* Update youtube_dl/downloader/external.py

Co-authored-by: dirkf <fieldhouse@gmx.net>
* refactoring code and fix bugs

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* Rename test_external_downloader.py to test_downloader_external.py

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Co-authored-by: dirkf <fieldhouse@gmx.net>