ASA: Replace vector processing with raster processing

**Describe the task**

There are a couple places in processing SFMS data where there is polygonizing and vector processing happening.

We could drastically speed up SFMS calculations by replacing these processes with raster only processing (masking).

We would need the convert fire zone units to rasters and use those as mask to pull information from SFMS rasters.

The result would be significantly faster processing, at the expense of some precision.

**Acceptance Criteria**
- [ ] Generate and store rasterised Fire Zone Units
- [ ] Raster resolution is 2 Km to match current SFMS rasters
- [ ] HighHFI/TPI/Combustible Area may have code/database tables to be removed

**Additional context**
- There may be other applications for raster-based zonal statistics in future versions of SFMS Insights.

Start by locating the SFMS data processing paths that currently polygonize fire zone units and perform vector processing. Define the rasterization and masking approach around the stated 2 Km resolution, then verify completion against the acceptance criteria, including whether the HighHFI, TPI, Combustible Area code or database tables can be removed.

Written by the indexing model from the issue text.