feat: add extra_assignments to build_function_wrapper

Author: AayushSabharwal

src/systems/codegen_utils.jl

@@ -108,10 +108,12 @@ generated functions, and `args` are the arguments.
   code for `expr`.
 - `wrap_mtkparameters`: Whether to collapse parameter buffers for a split system into a
   argument.
+- `extra_assignments`: Extra `Assignment` statements to prefix to `expr`, after all other
+  assignments.
 
 All other keyword arguments are forwarded to `build_function`.
 """
-function build_function_wrapper(sys::AbstractSystem, expr, args...; p_start = 2, p_end = is_time_dependent(sys) ? length(args) - 1 : length(args), wrap_delays = is_dde(sys), wrap_code = identity, add_observed = true, filter_observed = Returns(true), create_bindings = true, output_type = nothing, mkarray = nothing, wrap_mtkparameters = true, kwargs...)
+function build_function_wrapper(sys::AbstractSystem, expr, args...; p_start = 2, p_end = is_time_dependent(sys) ? length(args) - 1 : length(args), wrap_delays = is_dde(sys), wrap_code = identity, add_observed = true, filter_observed = Returns(true), create_bindings = true, output_type = nothing, mkarray = nothing, wrap_mtkparameters = true, extra_assignments = Assignment[], kwargs...)
     isscalar = !(expr isa AbstractArray || symbolic_type(expr) == ArraySymbolic())
     # filter observed equations
     obs = filter(filter_observed, observed(sys))
@@ -151,6 +153,7 @@ function build_function_wrapper(sys::AbstractSystem, expr, args...; p_start = 2,
     for eq in Iterators.flatten((cmap, pdeps[pdepidxs], obs[obsidxs]))
         push!(assignments, eq.lhs ← eq.rhs)
     end
+    append!(assignments, extra_assignments)
 
     args = ntuple(Val(length(args))) do i
         arg = args[i]