feat(logging): add customizable access log format for Gunicorn style …

[ZaneL1u]

Summary

This PR adds support for Gunicorn-style customizable access log formatting to Uvicorn, addressing issue #527 .

Users can now specify custom access log formats using the --access-log-format CLI option or the access_log_format parameter in the Python API, supporting 20+ format atoms compatible with Gunicorn's specification.

Changes

• New GunicornAccessFormatter class in uvicorn/logging.py

  • Supports 20+ Gunicorn format atoms (h, l, u, t, r, m, U, q, H, s, B, b, f, a, T, D, M, L, p)
  • Basic Authentication username extraction
  • Request header interpolation via %({header}i)s syntax
  • Response time tracking in multiple units

• CLI option --access-log-format

  • Example: uvicorn app:app --access-log-format '%(h)s %(l)s %(u)s %(t)s "%(r)s" %(s)s %(b)s "%(f)s" "%(a)s"'

• Python API parameter access_log_format

  • Added to Config class and run() function

• Protocol integration

  • Modified h11_impl.py and httptools_impl.py to track response time and size
  • Automatic formatter detection (GunicornAccessFormatter vs AccessFormatter)

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.