drop dependency on 'urllib3'

[jameslamb]

Closes #9267

distributed has a hard runtime dependency on urllib3 only for --preload (see #3755). That's only used for a single GET request with retries. This proposes replacing it with urllib from the standard library (h/t @jrbourbeau for the suggestion) and removing the urllib3 dependency.

Notes for Reviewers

• Tests added / passed
• Passes pre-commit run --all-files

I left one optional use in test-only code

Intentionally left this:

distributed/continuous_integration/scripts/test_report.py

Line 22 in d8fabe2

from urllib3.util.retry import Retry

And the dependency in the conda env for running that:

distributed/continuous_integration/scripts/test-report-environment.yml

Line 10 in d8fabe2

- urllib3

How I tested this

python -m venv .venv
source .venv/bin/activate

pip install \
  . \
  pytest \
  pytest-cov \
  pytest-repeat \
  pytest-rerunfailures \
  pytest-timeout

pytest ./distributed/tests/test_preload.py

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    31 files  ±0      31 suites  ±0   10h 41m 51s ⏱️ + 9m 9s
 4 074 tests ±0   3 967 ✅  -  3    104 💤 ± 0  2 ❌ +2  1 🔥 +1 
59 131 runs  ±0  56 648 ✅  - 50  2 480 💤 +47  2 ❌ +2  1 🔥 +1 

For more details on these failures and errors, see this check.

Results for commit 4876d19. ± Comparison against base commit d8fabe2.

[crusaderky]

Intentionally left this:
distributed/continuous_integration/scripts/test_report.py

That's fine, test_report.py is currently broken and needs a heavy maintenance pass anyway.

[crusaderky]

I've also tested this manually without mocks