gh-143445: Optimize deepcopy for 1.04x speedup (#143449)

Gains according to pyperformance:

```
deepcopy:
Mean +- std dev: 411 us +- 2 us -> 396 us +- 3 us: 1.04x faster
Significant (t=28.94)

deepcopy_reduce:
Mean +- std dev: 4.38 us +- 0.05 us -> 4.23 us +- 0.04 us: 1.04x faster
Significant (t=20.05)
```

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>