Replace custom line types with upstream implementation

[danielelerede-oet]

Changes proposed in this Pull Request

This PR replaces the downstream-specific implementation of US transmission line types with the country-specific framework introduced in PyPSA-Earth PR #1933.

Checklist

• I consent to the release of this PR's code under the AGPLv3 license and non-code contributions under CC0-1.0 and CC-BY-4.0.
• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented, including updates to docstrings for meaningful functions.
• Newly introduced dependencies are added to envs/environment.yaml and doc/requirements.txt.
• Changes in configuration options are added in all of config.default.yaml and config.tutorial.yaml.
• Add a test config or line additions to test/ (note tests are changing the config.tutorial.yaml)
• Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/user-guide/configuration.md and doc/tutorials/electricity-model.md.
• If config sections were added, renamed, or removed, update doc/assets/scripts/extract_config_snippets.py accordingly.
• Archives of the uploaded data do not have an enclosing folder and archive names correspond to the conventions of configs/bundle_config.yaml.
• A note for the release notes doc/release-notes.md is amended in the format of previous release notes, including reference to the requested PR.