Update to Catalyst 13 and latest Symbolics

[isaacsas]

This updates to the latest Catalyst (V13) and Symbolics. Please double check I understood what you wanted the Term in getsubstitutions to be -- Symbolics no longer uses Terms, and generally one shouldn't be directly constructing them or their new equivalent. It seemed like you wanted a vector of symbolic variables with a given symbol for their name, so that is what I replaced it with. I can update differently if needed.

Also, given Julia 1.6 is the latest LTS release I updated the Julia dependency to that. Most SciML packages only support 1.6 on now. (And will likely migrate up again soon if 1.10 or 1.11 becomes a LTS release.)

[codecov-commenter]

Welcome to Codecov 🎉

Once merged to your default branch, Codecov will compare your coverage reports and display the results in this comment.

Thanks for integrating Codecov - We've got you covered ☂️

[isaacsas]

I missed the doc examples need updating too. Will try to do that today.

[isaacsas]

This should hopefully fix the doc builds. Note that Documenter.jl recently released a (breaking) 1.0 version, so I set this to the last pre-1.0 version. You'll need some more updates to migrate to 1.0.

[isaacsas]

You should consider converting these at some point to @example blocks in the future, which will dynamically run the code when building the docs, and let you see if there is an issue with it.

[kaandocal]

Hi Sam, many thanks for your PR! I wanted to merge it yesterday but stumbled on the documentation bit. Merged!