fix: turn off parameter splitting for BifurcationProblem

[AayushSabharwal]

BifurcationProblem does not support symbolic indexing and as a result, MTK (somewhat hackily) just removes sys.index_cache in the BifurcationProblem constructor to force split = false behavior. However, with complete now reordering parameters, this breaks assumptions and makes analysis of these problems difficult.

In hindsight, BifurcationProblem should have just errored if the system was created with split=true, but changing that behavior is breaking. I will add a warning in MTK. For now, this should fix CI

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[isaacsas]

@AayushSabharwal just circling back to this now that Catalyst CI finally works again. Is this still needed? I think MTK's BifurcationKit extension was updated some since you submitted this to Catalyst?

[isaacsas]

I don't see split = true being used there at all (in the tests for example).

[AayushSabharwal]

It is still needed. complete with split = true (the default) reorders parameters. Since BifurcationProblem doesn't support symbolic indexing, the order matters for user accessibility.

[ChrisRackauckas]

We can just make BifurcationProblem support SII? That seems like the better long term solution here.

[AayushSabharwal]

I agree, this was written to get tests passing quickly. A quick look at BifurcationKit internals says it shouldn't be too difficult to support SII so I'll see what I can do.

[isaacsas]

Tests seem to pass now in either case. MTK seems to explicitly not set this though: https://github.com/SciML/ModelingToolkit.jl/blob/1f2d9430cfc6b7ebe2044dfb1b9a078eac4af87e/ext/MTKBifurcationKitExt.jl#L152

So that needs updating I guess (until BifurcationKit is made to work with SII)?