Support variable-length positional and keyword parameters in function passed to executor

[chuckwondo]

Fixes #1456

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[JosepSampe]

Thanks a lot for the contribution @chuckwondo ! Really appreciate you taking the time to identify and fix this.

[chuckwondo]

Thanks a lot for the contribution @chuckwondo ! Really appreciate you taking the time to identify and fix this.

Hi @JosepSampe. Again, my pleasure, and thank you for lithops and your responsiveness. Much appreciated!

[RichardScottOZ]

Yes, have used a ton recently, so thanks again!