refactor: small performance increases

[latonis]

• reduce allocations
• don't use format

[github-actions]

Benchmark Results

flatten_inputs/default/small
                        time:   [1.0288 µs 1.0296 µs 1.0308 µs]
                        thrpt:  [970.14 Kelem/s 971.24 Kelem/s 971.99 Kelem/s]
                 change:
                        time:   [-25.018% -24.432% -23.973%] (p = 0.00 < 0.05)
                        thrpt:  [+31.532% +32.331% +33.366%]
                        Performance has improved.
flatten_inputs/preserve_arrays/small
                        time:   [1.1709 µs 1.1756 µs 1.1803 µs]
                        thrpt:  [847.22 Kelem/s 850.64 Kelem/s 854.02 Kelem/s]
                 change:
                        time:   [-20.571% -20.090% -19.650%] (p = 0.00 < 0.05)
                        thrpt:  [+24.455% +25.141% +25.899%]
                        Performance has improved.
flatten_inputs/alt_array_flattening/small
                        time:   [1.1058 µs 1.1080 µs 1.1109 µs]
                        thrpt:  [900.17 Kelem/s 902.50 Kelem/s 904.35 Kelem/s]
                 change:
                        time:   [-23.945% -23.392% -22.950%] (p = 0.00 < 0.05)
                        thrpt:  [+29.787% +30.535% +31.484%]
                        Performance has improved.
flatten_inputs/default/medium
                        time:   [48.464 µs 48.497 µs 48.531 µs]
                        thrpt:  [20.606 Kelem/s 20.620 Kelem/s 20.634 Kelem/s]
                 change:
                        time:   [-27.059% -26.033% -25.223%] (p = 0.00 < 0.05)
                        thrpt:  [+33.732% +35.196% +37.098%]
                        Performance has improved.
flatten_inputs/preserve_arrays/medium
                        time:   [48.327 µs 48.344 µs 48.364 µs]
                        thrpt:  [20.676 Kelem/s 20.685 Kelem/s 20.693 Kelem/s]
                 change:
                        time:   [-24.604% -24.424% -24.263%] (p = 0.00 < 0.05)
                        thrpt:  [+32.035% +32.317% +32.633%]
                        Performance has improved.
flatten_inputs/alt_array_flattening/medium
                        time:   [48.364 µs 48.383 µs 48.404 µs]
                        thrpt:  [20.660 Kelem/s 20.668 Kelem/s 20.676 Kelem/s]
                 change:
                        time:   [-25.256% -24.917% -24.690%] (p = 0.00 < 0.05)
                        thrpt:  [+32.784% +33.186% +33.790%]
                        Performance has improved.
flatten_inputs/default/large
                        time:   [1.1337 ms 1.1351 ms 1.1368 ms]
                        thrpt:  [879.65  elem/s 880.94  elem/s 882.07  elem/s]
                 change:
                        time:   [-28.463% -28.242% -28.088%] (p = 0.00 < 0.05)
                        thrpt:  [+39.058% +39.358% +39.788%]
                        Performance has improved.
flatten_inputs/preserve_arrays/large
                        time:   [1.1436 ms 1.1483 ms 1.1542 ms]
                        thrpt:  [866.38  elem/s 870.82  elem/s 874.40  elem/s]
                 change:
                        time:   [-26.124% -25.888% -25.612%] (p = 0.00 < 0.05)
                        thrpt:  [+34.430% +34.931% +35.362%]
                        Performance has improved.
flatten_inputs/alt_array_flattening/large
                        time:   [1.1568 ms 1.1574 ms 1.1582 ms]
                        thrpt:  [863.39  elem/s 863.98  elem/s 864.49  elem/s]
                 change:
                        time:   [-24.956% -24.726% -24.507%] (p = 0.00 < 0.05)
                        thrpt:  [+32.463% +32.848% +33.256%]
                        Performance has improved.
flatten_collisions/collisions_default/10
                        time:   [1.7280 µs 1.7295 µs 1.7307 µs]
                        thrpt:  [577.79 Kelem/s 578.21 Kelem/s 578.71 Kelem/s]
                 change:
                        time:   [-28.956% -28.715% -28.512%] (p = 0.00 < 0.05)
                        thrpt:  [+39.884% +40.281% +40.758%]
                        Performance has improved.
flatten_collisions/collisions_alt_flatten/10
                        time:   [1.6652 µs 1.6690 µs 1.6729 µs]
                        thrpt:  [597.77 Kelem/s 599.15 Kelem/s 600.54 Kelem/s]
                 change:
                        time:   [-30.812% -30.353% -30.013%] (p = 0.00 < 0.05)
                        thrpt:  [+42.883% +43.581% +44.534%]
                        Performance has improved.
flatten_collisions/collisions_default/100
                        time:   [15.340 µs 15.385 µs 15.427 µs]
                        thrpt:  [64.822 Kelem/s 64.998 Kelem/s 65.187 Kelem/s]
                 change:
                        time:   [-34.197% -33.961% -33.764%] (p = 0.00 < 0.05)
                        thrpt:  [+50.975% +51.425% +51.969%]
                        Performance has improved.
flatten_collisions/collisions_alt_flatten/100
                        time:   [15.414 µs 15.442 µs 15.479 µs]
                        thrpt:  [64.602 Kelem/s 64.759 Kelem/s 64.875 Kelem/s]
                 change:
                        time:   [-32.051% -31.745% -31.429%] (p = 0.00 < 0.05)
                        thrpt:  [+45.834% +46.509% +47.169%]
                        Performance has improved.
flatten_collisions/collisions_default/1000
                        time:   [149.48 µs 149.61 µs 149.77 µs]
                        thrpt:  [6.6769 Kelem/s 6.6842 Kelem/s 6.6897 Kelem/s]
                 change:
                        time:   [-34.183% -34.019% -33.852%] (p = 0.00 < 0.05)
                        thrpt:  [+51.176% +51.560% +51.935%]
                        Performance has improved.
flatten_collisions/collisions_alt_flatten/1000
                        time:   [151.08 µs 151.14 µs 151.20 µs]
                        thrpt:  [6.6137 Kelem/s 6.6164 Kelem/s 6.6190 Kelem/s]
                 change:
                        time:   [-33.222% -32.977% -32.747%] (p = 0.00 < 0.05)
                        thrpt:  [+48.692% +49.203% +49.749%]
                        Performance has improved.

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Benchmarked on commit 870d423012cc83edee72ff21e2964151b18a981d