Fix Ruff linter violations across the codebase

[B0TAxy]

This PR addresses and fixes multiple Ruff linter warnings and errors to improve code quality and consistency across the project. The changes include:

• Adding missing tz parameters to datetime.now() calls to ensure timezone-aware datetimes (DTZ005).
• Replacing deprecated or discouraged patterns according to the active Ruff ruleset.
• Formatting code to comply with style rules (e.g., unused imports, quote styles, whitespace issues).
• General cleanup to reduce lint noise and prevent potential runtime issues.

No functional changes were made — these updates are strictly linter-related.

[yunzheng]

Thanks for the PR, the example scripts were long overdue for this.

I added some small suggestions.

[yunzheng]

There are still some tests failing when I run tox -e py3, could you look into this?

I think mainly due to some imports that have moved to global imports. If that caused the side effect I think for now it would be better to change it back and add a specific # noqa: flag to the inline import.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.95%. Comparing base (6e8c6db) to head (fe15422).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #172      +/-   ##
==========================================
+ Coverage   82.90%   82.95%   +0.05%     
==========================================
  Files          34       34              
  Lines        3592     3591       -1     
==========================================
+ Hits         2978     2979       +1     
+ Misses        614      612       -2     

Flag	Coverage Δ
unittests	82.95% <100.00%> (+0.05%)	⬆️

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[B0TAxy]

There are still some tests failing when I run tox -e py3, could you look into this?

I think mainly due to some imports that have moved to global imports. If that caused the side effect I think for now it would be better to change it back and add a specific # noqa: flag to the inline import.

You're right — I moved the imports back inside the functions since placing them at the top-level causes some tests to fail, though the exact reason isn't clear. The current version of Ruff doesn't flag these as violations, but newer versions do, so we should revisit this and possibly add # noqa once we upgrade.

[yunzheng]

LGTM