[std] Congestion control for catchunks

[pulsejet]

Current implementation is fixed window.

[AnoldGH]

What algorithms should we support? AIMD and Cubic?

I wonder if window size control should be made an independent module and separated from fetcher logic. It might be useful to other future apps as well.

[pulsejet]

For getting started, I'll suggest whatever has lower complexity (my recollection is not very good)

[AnoldGH]

For getting started, I'll suggest whatever has lower complexity (my recollection is not very good)

I have created a draft PR (actually through an accidental touch) #131 , which contains some basic window control/signalling functionalities. LMK if that's a good start