Geopandas backend for valve layer

[kbonney]

Summary

This PR continues work started in #451 by adding a GeoPandas backend plotting option for plot_valve_layer. This modernizes another important plotting function while also handling several issues with the function:

• When using the nx version of plot_valve_layer with the 'gpd' backend for plot_network the valves appear underneath the network (this is caused by a zorder issue).
• The nx valve layer plotting does not take into account vertices when choosing valve coordinates, which can cause mismatches when using the 'gpd' plot_network.
• The nx valve layer plotting would cause some unwanted artifacts in some cases.

Comparison plot:

Tests and Documentation

Added tests for previously untested plot_valve_layer function.

AI Disclosure

• No AI tools were used in this contribution

• I used AI tools in this contribution.

Acknowledgement

By contributing to WNTR, I acknowledge that I have reviewed the software quality assurance guidelines and agree to the following terms and conditions for my contribution:

1. I agree that my contributions are submitted under the Revised BSD License.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.
3. If code was generated using AI tools, I have disclosed the use of AI and reviewed all code for quality assurance, correctness, security, and licensing.

• I have read and agree to the above acknowledgement

Tests and Documentation

Added tests for previously untested plot_valve_layer function.

AI Disclosure

• No AI tools were used in this contribution

• I used AI tools in this contribution.

Acknowledgement

By contributing to WNTR, I acknowledge that I have reviewed the software quality assurance guidelines and agree to the following terms and conditions for my contribution:

1. I agree that my contributions are submitted under the Revised BSD License.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.
3. If code was generated using AI tools, I have disclosed the use of AI and reviewed all code for quality assurance, correctness, security, and licensing.

• I have read and agree to the above acknowledgement