fix shell completion for NP3

[jkowalleck]

TL;DR: fix shell completion for version 3.
its currently disabled for a reason.

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in upcoming verrsion 3 of nichtparasoup
the CLI will probably be driven via click instead of argparse

unfortunately click has a broken feature for shell autocompletion in version 7.

• file/path completions not implemented
  • File and path completion again pallets/click#1403
  • Tab completion behavior for click.File and click.Path types pallets/click#780
• named subcommands broken
  • fix completion for sub-command names pallets/click#1529
  • 7.x fix completion for sub-command names pallets/click#1598

see also: pallets/click#1622

it's fortunate that this will be fixed in version 8 - as far as the milestones give insignt.

an intermediate fix fia click_completion is incomplete, too: file completions are not working.

• file/path completions not implemented
• no option to manually implement them, since click's autocompletion funciton is not taken into account
  • Add autocompletion callback for Options click-contrib/click-completion#27
  • Add support for user autocompletion functions click-contrib/click-completion#34

[jkowalleck]

there was an attempt to use alternative click completion, already.
see https://github.com/k4cg/nichtparasoup/blob/218cc230024aa34facd8fc2e237b22ae8b639245/src/nichtparasoup/cli/completion._py