improve performance of recode! for array dest

[ahnlabb]

Performance improvements to fix #354.

Before:

  178.212 μs (47 allocations: 1.15 MiB)
  130.184 ms (1098374 allocations: 32.00 MiB)
  155.115 ms (998374 allocations: 28.95 MiB)
  154.162 ms (998378 allocations: 30.48 MiB)

After:

  191.479 μs (47 allocations: 1.15 MiB)
  187.252 μs (60 allocations: 394.39 KiB)
  1.384 ms (6 allocations: 288 bytes)
  1.689 ms (10 allocations: 1.53 MiB)

Todo:

• [ ] Benchmark other "shapes" of the data to ensure no regression for #345

[nalimilan]

Any news here?