Internal enhancements and improvements: optimize code and enable parallel processing capabilities

[amyburness]

Optimize code and enable parallel processing capabilities in Trends.Earth. This will decrease processing
times significantly. Ensure that code uses “QGSTasks” where appropriate so that tasks can more easily be parallelized, that users can view percentage completion, cancel tasks, etc. Also use the “numba” library as appropriate to ensure any processing code that
could benefit from just-in-time compilation does so.

[amyburness]

Deliverables for Internal enhancements and improvements :

• GUI element, element, e.g. modal window.
• Revised land cover processing algorithm.
• Optimized processing algorithm for speed
• CHIRPS dataset and national population dataset selectable from dropdown in GUI.
• Download tool updated to support additional filtering options and metadata display.
• UNCCD reporting tool including local dataset metadata.
• Unit tests added in codebase.