Prepare release 1.0.0

[davidorme]

This is to provide a meta issue as a checklist of things to do for a release 1.0.0:

• Drop Python 3.9 Remove support for Python 3.9 #196
• Testing milestone:
  • Adopt new unit tests, closing Add unit tests #23
• SPLASH milestone:
  • Close Fix time handling in SPLASH #165,
  • Close Verbose mode in SPLASH estimate_initial_soil_moisture doesn't handle np.nan #192
• Subdaily milestone:
  • Close Handling incomplete days at the start and end of time series in FastSlowScaler #72
  • Maybe close Allow FastSlowModel to take initial realised values #82 but this could hang on for a next release. (Finicky - going to wait for next release).
  • Check if NA handling in subdaily models etc #70 now covered and close.
  • Remove the previous subdaily version and move over to new implementation, closing Remove outdated FastSlowPModel #197
  • Rename FastSlowScaler (closed by Remove outdated FastSlowPModel #197)
• Profiling milestone - refactor of profile.py (closed by Update profiling/report.py and its documentation #188)
• Horner polyval (closed by Use a function eval_poly for polynomial evaluation #187)
• Adopt trusted publishing (Setup trusted publishing #198)
• Run a dummy release to test publishing
• Fix up the issues with the profiling system (closing Profiling issues #207)
• Fix up the issues with the profiling system again (closing Profiling workflow still broken #224 )
• Update CONTRIBUTING to remove duplication and order the material better (closing Development docs #209)
• Update CHANGES and README
• Update package metadata to add new authors etc.

The issue also has an associated release/1.0.0 branch which should be used for checking release candidates before merging into main and develop.