Benchmark for multiplechoicefield

[anjaniacatus]

This benchmark was added as part of the https://code.djangoproject.com/ticket/36913
Optimise ChoiceField / MultipleChoiceField handling of duplicate submissions

My conf for running the benchmark

{
  "version": 1,
  "project": "Django",
  "project_url": "https://www.djangoproject.com/",
  "repo": "https://github.com/anjaniacatus/django.git",
  "branches": ["ticket_36913"],
  "build_command": [
      "python -m pip install build",
      "python -m build --wheel -o {build_cache_dir} {build_dir}"
  ],
  "environment_type": "virtualenv",
  "show_commit_url": "http://github.com/anjaniacatus/django/commit/",
  "pythons": ["3.12", "3.13"]
}

cmd :
asv run --bench MultipleChoiceFieldValidate

for python3.12 : 1.26 ± 0.2ms --> 28.8 μs
for python 3.13 : 873 ± 200μs --> 28.1±3μs