gui: Display EPSG codes in tooltips for Data Catalog locations

[polucifier]

Description

This PR enhances the Data Catalog tree view by providing immediate spatial context to users. It displays the EPSG code via a native tooltip when hovering over a georeferenced project (location).

Technical Details

• Native Extraction: Uses g.proj -g inside a temporary isolated environment (gs.create_environment).
• Lazy Caching: The EPSG code is fetched once and cached in the node's internal data dictionary (data["epsg"]), ensuring that tree sorting and filtering remain instantaneous.
• Fallback: Safely returns None for unreferenced locations (like XY), rendering them without any extra markup.
• On-Demand Execution: The projection lookup is triggered exclusively by the wx.EVT_TREE_ITEM_GETTOOLTIP event. This ensures the heavy g.proj call only happens when the user actively hovers over a location, preventing any latency during application startup or tree initialization.

How to Test

1. Open the Data Catalog panel in the GRASS main window.
2. ​Hover the mouse cursor over any georeferenced project (location) name.
3. ​Verify that a native tooltip appears after a short delay showing EPSG:XXXX.
4. ​Verify that the tree interface remains responsive and that no errors are triggered in the console during hover.

Visuals

[ecodiv]

Would it be possible to make this optional? I can see why this is possibly handy, but for me it would add clutter.

[echoix]

Could it show up in the tooltip if it already doesn’t do it normally?

[echoix]

Having it optional, enable per project would avoid having to do these calls only for the GUI, (slowing down the initial loading). Similar to how the number of features of a layer isn’t systematically counted and displayed in QGIS, you have to enable it for the layer if wanted.

[petrasovaa]

#5294 and #7297 are related. I am honestly not sure this feature is needed...

[polucifier]

#5294 and #7297 are related. I am honestly not sure this feature is needed...

I feel like having this in a tooltip is more convenient and expected than calling "show projection info" from the context menu for each location or changing the current mapset to see the CRS in the status bar. It provides instant, zero-click access to the EPSG code just by hovering, which is faster when browsing through multiple projects.

If you think this alternative UX isn't needed, let me know and I will gladly close this PR. Thanks!