Make MaxWidthCellManager work with fixed signals

[leolara]

Currently only SingleRowCellManager can handle fixed signals. Make it work on MaxWidthCellManager.

Because the fixed signals use different columns than the other signals, we need a new parameter called max_width_fixed.

[atsupontio]

I would like to try working on this issue!

[leolara]

@atsupontio assigned

[atsupontio]

I dont know where a new parameter max_width_fixed should be added, should it be added to the MaxWidthCellManager structure and used separately from max_width?

Also, I have an implementation in my branch without max_width_fixed added.
I ran poseidon.rs with this implementation as let single_config = config(MaxWidthCellManager::new(2, true), SimpleStepSelectorBuilder {}); #78 and it worked fine.

Is there anything I should fix?

[leolara]

MaxWidthCellManager should have a new field called max_width_fixed, also rename max_width to max_width_advice.

https://github.com/privacy-scaling-explorations/chiquito/blob/main/src/plonkish/compiler/cell_manager.rs#L233

[atsupontio]

I added max_width_fixed and renamed max_width to max_width_advice.
There is implementation in my branch, so please take a look!
And, please let me know if anything else is required.

[leolara]

@atsupontio for us to review code has to be sent on a PR, it can be draft mode if you are unsure.