cache power reports

Check version

• I'm running the latest version of Path of Building and I've verified this by checking the changelog

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• I've checked for duplicate issues by using the search function of the issue tracker

Is your feature request related to a problem?

Power reports are extremely slow to generate, and they are often switched between even without modifying anything.

Describe the solution you'd like

A very simple cache would wok wonders for many use cases. You don't even need to be smart about caching sub-graph, just invalidate on modification. You could also keep a map of the build code to results for when edits are done and reverted often. I do that a lot, but I'm not sure how others use it. These are both pretty low impact changes I would think.

Describe alternatives you've considered

Rewrite in c++ probably isn't a great solution.

Additional context

Also, some progress indicator in a window footer for how much computation still needs to be done would be nice.

El issue no especifica archivos, pruebas ni un punto de entrada. Empieza por localizar el flujo de generación de power-report y determinar cómo se detectan las modificaciones del build; después, evalúa por separado el caching y el indicador de progreso solicitado. Se considera terminado cuando los reports repetidos sin cambios evitan cálculos innecesarios y el trabajo restante queda cubierto por una validación adecuada.