Catalyst V14 TODO

[TorkelE]

• MTK 9 compatibility and any needed new tests
• Update MTK tests with stuff that has gotten fixed in MTK.
• Add DSL option to control combinatoric_ratelaws
• Remove most mutating API functions (merge!, addspecies!, etc)?
• finalize new macro fields
• settle how complete will work (settled)
• Should we make conservation law removal of dependent species a non-mutating system transformation, more in line with how MTK does stuff? (will leave as is but perhaps turn on by default for ODE/SDE systems)
• Turn on conservation law removal by default for ODE/Nonlinear/SS systems. will leave off for now
• figure out how we should handle units (do we need more changes?)
• remove all instances where ordering of states or parameters is assumed with regard to initial conditions or parameter values (including across all tests and docs)
• fix mass action jump initialization (MTK)
• fix symbolic stoich tests involving jumps that use MTK internals to get rate/affect functions instead of getting them via JumpProblems. This will allow testing with propoer MTKParameter objects.
• add tests for mixed type parameters and make sure they work/fail appropriately (symbolic integer stoich for ex)
• fix broken jump test with binomials in higher order tests, and broken jump tests in reactionsystem tests
• check how to handle array variables now (stop scalarizing?)
• make sure noise scaling parameters/species/variables get added into systems via the two-argument constructor or the scaling transformation function.
• ensure all tests that are random use StableRNGs.
• Stop testing the v14 dev branch on CI.
• update docs thoroughly for v14 with regard to existing functionality (i.e. not new tutorials/features)
• update out-of-date stuff in coagulation tutorial
• Improve location of completeness description in docs.
• add migration guide for pre V14 users and make clear how breaking V14 is in the README too
• reenable formatter and format before release (but not till done with PRs...)
• fix v14 tests broken #824 and re-enable disabled tests associated with it.
• incorrect Float64 assumptions in diff_to_zero #825
• don't use internal Symbolics.jl functions #826
• add test for remaking parameters that are functions of other parameters (and updating them in general)
• check whether integer parameters in distributions work
• unitful working? (it doesn't, it will be problematic to sort out)
• DynamicQuantities working?
• update docs / HISTORY to make clear standard units no longer work.
• fix Latex display of equations with subscripts (as much as possible in Catalyst) (Post V14)
• figure out why plotting jump solution using saveat is so slow and update docs accordingly.
• update Catalyst to use "." instead of unicode + as the symbol separator.

Tracking PRs that are needed for Catalyst 14, including DSL updates. (@TorkelE can you order these in the suggested merge order if you have a chance?)

• [v14 ready] Implement metadata for Reactionss #749
• [v14 ready] Improve noise scaling implementation #678
• Handle test errors from MTKv9 update (including ReactionSystem completeness) #784
• Add reaction system metadata #783
• Change states to unknowns #785
• Use MTK's default t and D throughout repository #786
• Handle different parameters types #797
• Handle units #798
• Add MTK structure indexing tests #761
• Equations and events reupload #801
• Noise scaling update #800
• Drop mutating API functions and macro #823
• Add @combinatoric_ratelaws to DSL #828

There are a number of other doc updates, but most of them seem to be adding new docs/tutorials (instead of updating current docs for MTK9). I think we should get updates for V9 finished and then return to new tutorials.