SymbolicDiscreteCallback and SymbolicContinuousCallback are missing kwargs

[jonasmac16]

Hi,

I just discovered that both symbolic callbacks MTK.jl don't accept kwargs.

SymbolicContinuousCallback

ModelingToolkit.jl/src/systems/callbacks.jl

Line 73 in a69570a

struct SymbolicContinuousCallback

SymbolicDiscreteCallback

ModelingToolkit.jl/src/systems/callbacks.jl

Line 150 in a69570a

struct SymbolicDiscreteCallback

This means arguments such as save_positions can't be passed to these callbacks in MTK.