Masking strategies based on healpix cells

[shmh40]

Is your feature request related to a problem? Please describe.

Current masking is random over a 1D flattened array of cells.

Describe the solution you'd like

Implement methods to mask based on healpix level - e.g. masking whole healpix cells at arbitrary levels.

Describe alternatives you've considered

No response

Additional context

No response

Organisation

No response

[shmh40]

This is mostly implemented now in shmh40/dev/masking_strategies.