Eagerly perform set insertions in nub{Ord,Int}

[meooow25]

Currently we create thunks for at every step that get forced at the next step when we check for set membership. Here we change the insertions to be eager. This means doing a bit of work upfront that would otherwise be pushed to the next step but without the overhead of creating a thunk for it, which reduces a noticeable amount of allocations overall.

The go functions can also be marked as strict in the input set now.

Benchmarks on GHC 9.14 show a decrease in allocations of 8% on nubOrd.noFusion_distinct and nubOrd.strings_noFusion_distinct.

---

Name                                Time - - - - - - - -    Allocated - - - - -
                                         A       B     %         A       B     %
nubOrd.issue1202_distinct            46 μs   42 μs   -8%    672 KB  618 KB   -8%
nubOrd.issue1202_repeat             4.0 μs  3.9 μs   -2%     16 KB   16 KB   +0%
nubOrd.noFusion_distinct             44 μs   39 μs   -9%    633 KB  579 KB   -8%
nubOrd.noFusion_repeat              1.8 μs  1.3 μs  -28%    152 B    96 B   -36%
nubOrd.strings_noFusion_distinct    114 μs  112 μs   -1%    626 KB  572 KB   -8%
nubOrd.strings_noFusion_repeat      4.2 μs  4.0 μs   -4%    154 B    98 B   -36%