feat: add function to merge low voltage to market node

[lisazeyen]

Closes # (if applicable).
#722

Changes proposed in this Pull Request

Merge in the CBA the low voltage nodes and the high voltage nodes to only have market model nodes

Tasks

Workflow

in simplify_sb_network.py a new function is added which attaches all the assets connect to the low voltage buses to the high voltage buses, removes the low voltage load shedding, removes all the links which are connecting then to the same bus in bus0 + bus1 (distribution grid links after the mapping), removes the low votlage buses

Open issues

• how generic to we need the function. Currently location column is used for the mapping (advantage: very little code to create the busmap, hopefully reusable for H2 Zones) which might fail for other bus carriers (then one would one to define a busmap directly).

Notes

• one should keep in mind that the added function might be used also for merging the H2 Zones in a later stage, function should be easy to generalise on this use-case.

Checklist

Required:

• Security scans show no high-severity bugs, critical vulnerabilities, or exposed secrets.
• Changes are tested locally and behave as expected.
• Code and workflow changes are documented.
• A release note entry is added to doc/release_notes.md.
• The description is human-written and any AI-generated content is marked.

If applicable:
- [ ] Changes in configuration options are reflected in scripts/lib/validation.
- [ ] Changes in configuration options are added to config/test/*.yaml.

• Multiple climate years test passes locally (pixi run -e open-tyndp tyndp-cyears-test).
  - [ ] For new data sources or versions, these instructions have been followed.
  - [ ] Open-TYNDP SPDX license header is added to all touched files.
• Module docstrings are added to new Python scripts.
  - [ ] New rules are documented in the appropriate doc/*.md files.
  - [ ] Major features are documented in doc/index.md.

[daniel-rdt]

Thank you @lisazeyen. I tested the implementation and it looks to be working as intended. The effects are already visible in the required RAM (see test run results here). It is not clear to me yet, how large the performance speed ups of this are, if any.

Otherwise, I have just a couple of comments for the docstring and cleaning up the code a tiny bit.

[lisazeyen]

thanks @daniel-rdt I applied the suggested changes + added a release note.

[daniel-rdt]

Thank you @lisazeyen! Looks good to me. Only one minor note to update one of the comments. Then gtg for me :)