Atomica

- Added methods `ParameterSet.calibration_spreadsheet()`, `ParameterSet.save_calibration()` and `ParameterSet.load_calibration()` to allow saving calibration scale factors to spreadsheets that can be edited externally.

- Fix plotting routines that were previously checking for missing timescales by checking for `None` values, and were thus missing `np.nan` values. This change was introduced around version 1.24.1 when framework validation now guarantees that the parameter timescale is a numeric type. This causes missing timescales to be populated with `nan` rather than `None`.
- Add library framework for malaria

*Backwards-compatibility notes*

- Any code checking for missing timescales by checking for a `None` value should instead use `pd.isna()` to check for `nan` _or_ `None` values

- Fixes a bug in validation that ensures parameters in 'proportion' units cannot have a timescale. Previously frameworks with this error would incorrectly pass validation

- Added validation of plots sheet in framework file
- Allow validating a framework multiple times
- Fix an edge case with timed transitions and split transition matrices

*Backwards-compatibility notes*

- In rare cases, if an existing framework file contains an error that was not previously detected, it may now produce an error when loaded. Such errors indicate problems in the framework that should be debugged as usual.

- Fix bug where program outcomes were not correctly applied if overwriting a function parameter that does not impact any transitions

- Added `at.stop_logging()` and an optional `reset` argument to `at.start_logging()`