Omnibus of Performance & Testing Improvements

[aphyr]

I can't keep the separate git branches straight any more, and from our earlier conversation it sounds like you're amenable to a suite of fixes, so here's a single PR.

As a side note, there's some kind of failure in sorted-map-slice and int-map-slice that seems pre-existing... not sure what's up with that exactly.

FAIL in (test-sorted-map-slice) (collection_test.clj:504)
expected: {:result true}
  actual: {:shrunk
           {:total-nodes-visited 26,
            :depth 25,
            :pass? false,
            :result false,
            :result-data nil,
            :time-shrinking-ms 264,
            :smallest [1 1]},
           :failed-after-ms 8,
           :num-tests 1,
           :seed 1700069068231,
           :fail [6822 4794],
           :result false,
           :result-data nil,
           :failing-size 0,
           :pass? false,
           :test-var "test-sorted-map-slice"}
FAIL in (test-int-map-slice) (collection_test.clj:480)
expected: {:result true}
  actual: {:shrunk
           {:total-nodes-visited 26,
            :depth 25,
            :pass? false,
            :result false,
            :result-data nil,
            :time-shrinking-ms 252,
            :smallest [1 1]},
           :failed-after-ms 19,
           :num-tests 1,
           :seed 1700068598677,
           :fail [4682 4819],
           :result false,
           :result-data nil,
           :failing-size 0,
           :pass? false,
           :test-var "test-int-map-slice"}