Garbage collection frequency

[wlandau]

Prework

• I understand and agree to help guide.
• I understand and agree to contributing guide.
• New features take time and effort to create, and they take even more effort to maintain. So if the purpose of the feature is to resolve a struggle you are encountering personally, please consider first posting a "trouble" or "other" issue so we can discuss your use case and search for existing solutions first.

Proposal

Make it possible to only run garbage collection every n'th target, where n is set by the user.

[wlandau]

Done. Users can now set e.g. tar_option_set(garbage_collection = 100) to run gc() every hundredth target. This should balance memory and speed.