Simplify fromDistinct{Asc,Desc}List for Set, Map

[meooow25]

Uses only the Stack, making FromDistinctMonoState unnecessary. This implementation also allows for quick access to the last element, which may be used in fromAscListWith, mapKeysWith, etc.

Seems to be slightly faster. Benchmarks on GHC 9.6.3:

Before

Set
  fromDistinctAscList:         OK
    21.4 μs ± 1.3 μs, 224 KB allocated, 4.4 KB copied, 8.0 MB peak memory
  fromDistinctAscList:fusion:  OK
    21.0 μs ± 1.5 μs, 288 KB allocated, 7.6 KB copied, 8.0 MB peak memory
  fromDistinctDescList:        OK
    21.5 μs ± 840 ns, 224 KB allocated, 4.4 KB copied, 8.0 MB peak memory
  fromDistinctDescList:fusion: OK
    20.5 μs ± 1.4 μs, 288 KB allocated, 7.9 KB copied, 8.0 MB peak memory

Map
  fromDistinctAscList:         OK
    28.5 μs ± 2.8 μs, 271 KB allocated, 6.7 KB copied, 9.0 MB peak memory
  fromDistinctAscList:fusion:  OK
    23.8 μs ± 1.6 μs, 336 KB allocated,  10 KB copied, 9.0 MB peak memory
  fromDistinctDescList:        OK
    30.6 μs ± 2.8 μs, 271 KB allocated, 6.7 KB copied, 9.0 MB peak memory
  fromDistinctDescList:fusion: OK
    23.5 μs ± 702 ns, 336 KB allocated,  10 KB copied, 9.0 MB peak memory

After

Set
  fromDistinctAscList:         OK
    21.8 μs ± 1.4 μs, 223 KB allocated, 4.3 KB copied, 8.0 MB peak memory,       same as baseline
  fromDistinctAscList:fusion:  OK
    18.8 μs ± 1.4 μs, 288 KB allocated, 7.6 KB copied, 8.0 MB peak memory, 10% less than baseline
  fromDistinctDescList:        OK
    22.9 μs ± 1.7 μs, 223 KB allocated, 4.4 KB copied, 8.0 MB peak memory,       same as baseline
  fromDistinctDescList:fusion: OK
    18.8 μs ± 1.5 μs, 288 KB allocated, 8.0 KB copied, 8.0 MB peak memory,  8% less than baseline

Map
  fromDistinctAscList:         OK
    26.9 μs ± 1.8 μs, 272 KB allocated, 6.6 KB copied, 9.0 MB peak memory,       same as baseline
  fromDistinctAscList:fusion:  OK
    20.6 μs ± 1.5 μs, 336 KB allocated,  10 KB copied, 9.0 MB peak memory, 13% less than baseline
  fromDistinctDescList:        OK
    26.5 μs ± 1.4 μs, 272 KB allocated, 6.6 KB copied, 9.0 MB peak memory, 13% less than baseline
  fromDistinctDescList:fusion: OK
    20.7 μs ± 1.4 μs, 336 KB allocated,  10 KB copied, 9.0 MB peak memory, 11% less than baseline

[meooow25]

This is a tweak to the implementation I added in #950, motivated by reasons mentioned above (simpler IMO, access to last element).
Don't think there is much to be discussed here, but let me know if you think otherwise @treeowl.