Atomica

- Improve exported results link labelling for transfers

- Implemented variable total spend in `SpendingPackageAdjustment`
- Optimized performance for `SpendingPackageAdjustment` if proportions are fixed by adding a `fix_props` flag that skips adding `Adjustables` for the proportions
- Improved framework validation robustness when dataframe cells contain NA-like values (`np.nan` or `pd.NA`) instead of just `None`

- Program number eligible defaults to 0 if target compartments are missing (rather than raising a key error)
- `ProgramSet` spreadsheet constructor is now a class method to allow inheritance
- Fixed bug where program overwrites that impact a transition parameter via at least one intermediate parameter did not impact outcomes
- Improved `SpendingPackageAdjustment` performance although varying total spend is not yet supported

- Fix bug in program fractional coverage where not all programs were constrained to a peak coverage of 1

- Update calls to `sc.asd()` to be compatible with Sciris v1.2.3
- Update installation instructions to use `pip` rather than `setup.py` directly
- Improve handling of unspecified timescales in plotting routines

- Unfreeze `pandas` dependency because they have fixed some regressions that affected `atomica`