feat: support modern-di 4

[lesnik512]

Refs modern-python/modern-di#579.
Closes #42

Summary

• Widen the requirement to modern-di>=3.1,<5.
• tests/test_lifespan.py: test_restart_reopens_without_warning filtered exceptions.ContainerClosedWarning, which modern-di 4.0 removes. The test is now test_restart_reopens_root. It enqueues a job for the second worker cycle and asserts the job result. In 4.0 a resolve from a closed root raises ContainerClosedError, so the job fails if on_startup stops reopening the root. The old version ran no job in the second cycle, so it never resolved anything from the reopened root.

Verification

• 3.x (modern-di 3.6.0 from PyPI): eof-fixer, ruff format/check and ty pass; pytest 22 passed, coverage 100%.
• 4.0 (modern-di main f300c2e from a local wheel): ty passes; pytest 22 passed, coverage 100%.
• With container.open() removed from on_startup, the new test fails under 4.0 because the job raised ContainerClosedError.

This PR stays a draft until modern-di 4.0.0 is on PyPI.