Enable custom parseRunOptions

[BrtqKr]

Feature request
Either:

1. remove defining parseRunOpts as private - it's only a type definition and it would be great to be able to customize that behavior without errors
2. allow customizing actArguments used on parseRunOpts level

Additional context
First of all, thank you for this library 🙏

We're creating a class extending Act and right now we are overriding parseRunOpts, which is defined as private only on a .d.ts level, which causes errors, but doesn't restrict anything. I think it would be great to have more freedom in customizing how parse is done if someone decides to go further in using Act class only as a base.

https://github.com/Expensify/App/blob/main/workflow_tests/utils/ExtendedAct.js

[shubhbapna]

I see. I am a bit hesitant on making parseRunOpts public since if someone who wants to extend Act overrides parseRunOpts but forgets to call super or conflict with some of the stuff super.parseRunOpts does, it will break Act for them.