Fix Symbolic Indexing with Nums.

[MasonProtter]

The MTKExt package extension had some out of date dispatches that were stopping symbolic indexing with Nums from working.

e.g.

using Neuroblox, GraphDynamics, SymbolicIndexingInterface

let
    @named osc1 = HarmonicOscillator()
    @named osc2 = HarmonicOscillator()
    
    g = GraphSystem()
    add_connection!(g, osc1, osc2; weight=1.0)
    add_connection!(g, osc2, osc1; weight=1.0)
    sim_dur = 1e1
    prob = ODEProblem(g, [], (0.0, sim_dur),[])
    
    getp(prob, osc1.ω)(prob)
end

Before:

ERROR: Invalid symbol osc1₊ω for `getp`
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:44
 [2] _getp(sys::ODEProblem{…}, ::ScalarSymbolic, ::ScalarSymbolic, p::Num)
   @ SymbolicIndexingInterface ~/.julia/packages/SymbolicIndexingInterface/vXqJR/src/parameter_indexing.jl:368
 [3] getp(sys::ODEProblem{…}, p::Num)
   @ SymbolicIndexingInterface ~/.julia/packages/SymbolicIndexingInterface/vXqJR/src/parameter_indexing.jl:41
 [4] top-level scope
   @ REPL[18]:11
Some type information was truncated. Use `show(err)` to see complete types.

after

0.15707963267948966