[BUG] Missing pytz in package dependencies causes ModuleNotFoundError #365

Description

plotly-resampler imports pytz in plotly_resampler/aggregation/plotly_aggregator_parser.py (line 8), but pytz is not declared as a dependency in pyproject.toml.

This causes ModuleNotFoundError: No module named 'pytz' in clean environments (e.g., CI, Docker, fresh virtualenvs) where pytz is not installed as a transitive dependency of another package.

Reproducing the bug

# In a clean virtualenv
pip install plotly-resampler==0.11.0
python -c "from plotly_resampler import FigureResampler"

Traceback (most recent call last):
  ...
  File ".../plotly_resampler/aggregation/plotly_aggregator_parser.py", line 8, in <module>
    import pytz
ModuleNotFoundError: No module named 'pytz'

Root cause

plotly_aggregator_parser.py has import pytz at line 8, but pyproject.toml [tool.poetry.dependencies] does not include pytz.

Suggested fix

Either:

1. Add pytz = ">=2020.1" to [tool.poetry.dependencies] in pyproject.toml
2. Or replace pytz usage with datetime.timezone (stdlib, no external dependency needed)

Environment information

• Python version: 3.12
• plotly-resampler version: 0.11.0
• OS: Ubuntu (GitHub Actions runner)