Allow providing the max batch size as a cli arg

[brianmcgee]

Is your feature request related to a problem? Please describe.

Currently, all batching is hard coded to a maximum of 1024. In certain circumstances, it might be beneficial to specify smaller batch sizes to improve concurrency.

Describe the solution you'd like

Add a cli arg, --batch-size which controls the max batch size.

[zimbatm]

Another one related to this; we have a lot of tools that can only format a single file at the time.

We could replace a lot of those for file in "$@"; run_formatter "$file"; done bash wrappers with batch_size=1.

[brianmcgee]

Yeah, worth revisiting this. I'll have some time for treefmt at the end of this week. It would be nice to get this in before releasing #571

[zimbatm]

If we want to push the spec a bit more, we could be obnoxious with the setting names on purpose. incompatible_rule_1_single_file_workaround = true :-)