highlighted changes
1. change the type of these CUBIC windows to uint32_t from uint64_t
2. sync to the updated formulas in RFC9438 and carefully handles these
units (segments or bytes)
3. remove un-used function reno_cwnd()
change detail in cc_cubic.h
1. Updated `cubic_k` with the new formula in the RFC. It additionally
uses `cwnd_epoch` for calculating `K`.
2. Also updated these theoretical formula functions in userland.
change detail in cc_cubic.c
1. cubic_cong_signal() now just flag the event and let the epoch
start/re-start at the beginning of the current congestion avoidance
phase in cubic_ack_received().
2. Increase the cwnd only by `(target - cwnd) / cwnd` with a restrictive
`target` formula from the RFC. This shall further smooth the cwnd
growth, as observed in the default stack.
3. Remove the obsolete hack for probing `W_max` in early congestion
avoidance phase if used an old cwnd from hostcache.
4. Also remove the obsolete hack that aligns the concave region after
the first congestion event.