Scripts: Use PEP 723 inline metadata to declare dependencies

[NMertsch]

Some of the Python scripts in scripts/ require packages to be installed (e.g. discord.py or pydantic).

Let's use inline script metadata (PEP 723) to embed these requirements in the script files.

Many common tools already support this, including uv: uv run some-script.py will automatically create a temporary virtual environment with the embedded requirements, and use it to run the script.

(pip does not yet support it, though: pypa/pip#12891.)

Example:

# /// script
# requires-python = ">=3.9"
# dependencies = ["pydantic>=2.11.4"]
# ///
import pydantic

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