The previous values of the BSR timers would "starve" the UE: to my
understanding, constant UL traffic would not make any BSR timer expire,
and thus, no new BSRs were sent by the UE. However, since they were too
infrequent, the gNB thought there was no data anymore after serving the
UE for some slots.  Hence, reduce the timers to have constant UE buffer
feedback. Maybe they have to be increased if we ever have many UEs...

The TDA change used a binary search (worst case O(log n)) for finding
the right amount of RBs, whereas everywhere else we used a linear search
(O(n)). We generalize the binary search into a function nr_find_nb_rb()
and use it for DL and UL allocation.

Note: Need to maintain same PDSCH and PUSCH TDA list lengths

If the PDSCH and PUSCH TDA lists have different lengths (before this
commit, PDSCH TDA list length was 2, for PUSCH 3), the OAI UE would get
confused: In the special case, the TDA in the DCI for UL was incorrectly
calculated, and a change of the PDSCH TDA list triggered UL never being
decoded correctly.

The TBS calculation is necessary to implement the PF coefficient. To
avoid having to recalculate TDA and DMRS parameters for every UE that we
compare, we pre-calculate (approximate) TB sizes which can be used to
calculate the coefficient.

Until this commit, all user scheduling functionality would search for
the search space and CORESET in every TTI for UL&DL, over and over
again. This commit sets it once in add_new_nr_ue(), and the rest just
uses whatever search space/CORESET is set.

Introduce initialization functions for the FR1 preprocessors: they
can/will be used to pre-compute values needed during UE scheduling.

Add parameters: MCS, Bandwidth (in PRBs), slot scheduling bitmap

To shorten pf_ul() and make it more readable, we put the functionality
of retransmittiong to a UE into a separate function. Thus, it might be
re-used in other scheduling scheme functions (e.g., RR instead of PF).