Update tzlocal to v4.x and remove pytz dependency - #1528

Changes

• remove pytz dependency and replace it with zoneinfo from stdlib (rationale: https://pytz-deprecation-shim.readthedocs.io/en/latest/index.html)
• update tzlocal

Caveats

There are some differences between pytz's is_dst and datetime's fold argument: https://pytz-deprecation-shim.readthedocs.io/en/latest/migration.html#semantic-differences-between-is-dst-and-fold

I had to adapt a test for this. I don't know what the implications of this would be for jrnl. Please decide if this is reasonable for you.

Closes: #1338

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.