Switch to Python 3.14

[zaneselvans]

Overview

This issue tracks the process of updating PUDL to use Python 3.14, which was released in the fall of 2025.

• Somewhat faster.
• Better error messages.
• Better type annotations.
• Early free-threading support.

Blocking concerns

• dagster-dbt doesn't yet support Python 3.14
• The first version of pyarrow that works with Python 3.14 is v21, but Kaggle's very old geopandas 0.14 needs pyarrow v20.