gh-96859: [argparse] Avoid copying lists on every append and extend action

[alexeypa]

Currently the append, append_const, and extend actions make a copy of the target list every time the action is called. It becomes rather slow with very long option lists. This commit updates parse_known_args() to only copy on the first action call.

Using the repro script from the issue description I could see the following results before and after this change.

Before:

➜  cpython git:(c00964ecd5) ✗ ./repro.py                                      
     256 iterations: 0:00:00.002216 s
     512 iterations: 0:00:00.003734 s
    1024 iterations: 0:00:00.009686 s
    2048 iterations: 0:00:00.018806 s
    4096 iterations: 0:00:00.048392 s
    8192 iterations: 0:00:00.130792 s
   16384 iterations: 0:00:00.399441 s
   32768 iterations: 0:00:01.341005 s
   65536 iterations: 0:00:05.148916 s
  131072 iterations: 0:00:20.325517 s

After:

➜  cpython git:(gh-96859_take3) ✗ ./repro.py                   
     256 iterations: 0:00:00.002016 s
     512 iterations: 0:00:00.003760 s
    1024 iterations: 0:00:00.006729 s
    2048 iterations: 0:00:00.013103 s
    4096 iterations: 0:00:00.026316 s
    8192 iterations: 0:00:00.053061 s
   16384 iterations: 0:00:00.099570 s
   32768 iterations: 0:00:00.191617 s
   65536 iterations: 0:00:00.403077 s
  131072 iterations: 0:00:00.781361 s

• Issue: argparse.ArgumentParser is slow when parsing a very long option list #96859

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[serhiy-storchaka]

Thank you @alexeypa, but I do not like moving action-specific code to general code. I think that simple approach (#124909) would work as well.