Update compareSize implementations

[meooow25]

The previous implementations went straight down the left spine, which does not match the documented complexity. We must decrement and potentially return at each step to meet O(min(n,c)).

Also add some benchmarks for size and compareSize.

For #826.

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Benchmarks on GHC 9.10.1:

IntMap

Name             Time - - - - - - - -    Allocated - - - - -
                      A       B     %         A       B     %
compareSize:2     25 ns  6.0 ns  -76%     24 B    24 B    +0%
compareSize:n    7.4 μs  7.3 μs   -1%     36 B    35 B    -2%

IntSet

Name                    Time - - - - - - - -    Allocated - - - - -
                             A       B     %         A       B     %
compareSize:2            16 ns  6.4 ns  -60%     24 B    24 B    +0%
compareSize:n           255 ns  270 ns   +5%     32 B    32 B    +0%
compareSize:sparse:2     28 ns  6.4 ns  -76%     24 B    24 B    +0%
compareSize:sparse:n     17 μs   18 μs   +4%     35 B    40 B   +14%