fix(nrLDPC_coding): timers in DL encoding, fix(ldpctest): Confusion in sizes

Main improvements:

1. fix(ldpctest): Confusion in sizes
   IMPORTANT: This fix makes that ldpctest now works with BG2 and K' != K!
   (Worth double checking with more cases than I did check with though)
   The variable block_length had an ambiguous role and was used as both K and Kprime.
   This was leading to arrays with wrong sizes and functions with wrong arguments.
   Now there is not anymore block_length but K and Kprime.
   Kprime can be set with the command line argument -l.
   There was also some problems with array allocation for segments with length not divisible by 8.
   A proper sizing with ((size_in_bits + 7) & ~7) / 8 was used.
   A proper masking of the last byte containing payload bits was also added to keep filler bits to 0 after random initialization.

2. fix(nrLDPC_coding): timers in DL encoding
   While timers were available for rate matching and interleaving in the new interface,
   these timers were not merged to rate matching and interleaving timers in nr_dlsch_coding.