Draft: Build tree manually to discard low importance paths prematurely

[ogxd]

With sequences

14:55:07 [INFO] Garbage collection done in 3.48 ms
14:55:07 [INFO] Graph built in 17.638 ms
14:55:07 [INFO] Tree built in 5.24 ms
14:55:07 [INFO] Tree sorted in 15.876 ms
14:55:07 [INFO] Report written in 30.628 ms

Building the graph of linear sequences takes quite some time to compute, even though not all data will be needed afterward. Discarding early would speed up the whole process significantly. The problem is that at this stage we don't know yet the number of occurrences of a given retention path (it's in fact what this stage is supposed to do), so we can't discard in advance based on the number of occurrences. What can be done however is, instead of retrieving the full retention paths and then looking at several occurrences, drill through paths one level at a time, and discard at each level.

Without sequences (manual tree build + early discard)

wip