Adjusted the automated node placement

[Zetison]

This PR adjusts the following:

• If coordinates have not been saved to a design file for the nodes under an Area, they are now placed symetrically around the circle (that is, acounting for one node being the GeoAvailability node to be placed at the center). This is illustrated well by comparing changes to the docs/src/figures/EMI_geography_Oslo.png file.
• The default value for the radius of the circle for placing nodes without coordinates is now a third of the minimal distance between area coordinates defined in the top_level design file.

[Copilot]

Pull request overview

Adjusts automated node placement so that, when child node coordinates are not stored in the design file, the nodes are arranged on a circle accounting for the central availability node, and the default circle radius is derived from the minimum inter-area distance at the top level.

Changes:

• In setup_topology.jl, attempt to load x/y for each child from the saved design file before falling back to lon/lat, and compute radius = min_dist / 3 from those coordinates.
• Subtract one from nodes_count when placing nodes whose parent is a SystemGeo, to account for the centered GeoAvailability node.
• Update place_nodes_in_circle docstring parameter names and use explicit Float32 conversions in the angle computation.

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 1 comment.

File	Description
src/setup_topology.jl	Reorders initialization, adds design-file coordinate loading for SystemGeo, and adjusts nodes_count for the central availability node.
src/utils_gen/structures_utils.jl	Aligns docstring parameter names with the function signature and uses explicit Float32 in the angle computation.
NEWS.md	Adds an unversioned release note describing the placement adjustments.

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