feat: refactors temporal aggregation as a separate rule

[tgilon]

Closes # (if applicable).

Changes proposed in this Pull Request

This PR introduces a new distinct rule to apply the time aggregation on the time-varying network data. To achieve this:

• It refactors the temporal aggregation of a sector-coupled model as a separate rule,
• It renames previous temporal_aggregation as build_snapshot_weightings, and
• It introduces a new rule temporal_aggregation after prepare_sector_network that effectively applies the aggregation.

The benefit of doing this is that it makes the prepared network more explicit at hourly resolution.

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to pixi.toml (using pixi add <dependency-name>).
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.

[fneum]

This PR would not be compatible with the approach proposed in #1838. @FabianHofmann presented this today and to me it looks like #1838 would be preferable (without having reviewed the code in detail yet) as it elegantly unifies overnight, myopic, and perfect foresight code.

I would give that PR priority. One could always export the hourly model for reference as additional output. I will keep it open for now but close if #1838 gets merged.