Cleanup event finding and change nudging condition

[dcourteville]

While implementing the change in nudging condition for #1245, I somehow ended up cleaning up all the event finding code to remove the redundant computations and useless branches, and factorize some code between ContinuousCallback and VectorContinuousCallback. If I didn't break anything it should make maintaining the code easier.
I know I shouldn't make two changes in one PR, I can split into two PR if its an issue.

[ChrisRackauckas]

Draft?

[dcourteville]

I'll update the doc for abstol in SciMLBase

[ChrisRackauckas]

Null problem with callbacks: Test Failed at /home/runner/work/DiffEqBase.jl/DiffEqBase.jl/test/downstream/null_de.jl:165
  Expression: solve(prob_with_cb, Tsit5(); callback = cb)
    Expected: Exception
  No exception thrown

Stacktrace:
 [1] top-level scope
   @ ~/work/DiffEqBase.jl/DiffEqBase.jl/test/downstream/null_de.jl:151
 [2] macro expansion
   @ /opt/hostedtoolcache/julia/1.12.4/x64/share/julia/stdlib/v1.12/Test/src/Test.jl:1776 [inlined]
 [3] macro expansion
   @ ~/work/DiffEqBase.jl/DiffEqBase.jl/test/downstream/null_de.jl:165 [inlined]
Null problem with callbacks: Test Failed at /home/runner/work/DiffEqBase.jl/DiffEqBase.jl/test/downstream/null_de.jl:181
  Expression: init(prob_with_cb, Tsit5(); callback = cb)
    Expected: Exception
  No exception thrown

update those, downstream now handles that so it just needs to be set to passing. we will need to see downstream tests because they have a lot of callback stuff

[dcourteville]

Can this be merged or is there some other issues ?

[ChrisRackauckas]

This seemed to have some uncaught downstream consequences:

• DiffEqBase@6.201 broke callbacks #1268
• Removal of determine_event_occurence in DiffEqBase v6.201.0 broke DiffEqGPU precompilation #1267

I can handle the GPU things, that's from using non-public API in DiffEqGPU. But the MWE @AayushSabharwal found seems more central as a repeat callback detection failure. I think because of how much stuff looks breaking right now, it might be good to revert, figure out the repeat callback, and then re-merge, and I'll get the GPU update setup and ready for that. @dcourteville can you look into that repeat callback issue?