Use DEFAULT_SPECIALIZATION for NonlinearFunction constructors

Change NonlinearFunction constructors to use DEFAULT_SPECIALIZATION
(which defaults to AutoSpecialize via Preferences) instead of hardcoded
FullSpecialize. This matches the intended behavior where AutoSpecialize
is the default specialization level.

When NonlinearSolve.jl reads the AutoSpecialize trait, it wraps the
function in FunctionWrappers to eliminate per-function recompilation.
Without NonlinearSolve.jl#838, AutoSpecialize is a no-op (the trait
is stored but never read), so this change is backwards compatible.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

src/scimlfunctions.jl

@@ -4480,11 +4480,11 @@ function NonlinearFunction{iip, specialize}(
 end
 
 function NonlinearFunction{iip}(f; kwargs...) where {iip}
-    return NonlinearFunction{iip, FullSpecialize}(f; kwargs...)
+    return NonlinearFunction{iip, DEFAULT_SPECIALIZATION}(f; kwargs...)
 end
 NonlinearFunction{iip}(f::NonlinearFunction; kwargs...) where {iip} = f
 function NonlinearFunction(f; kwargs...)
-    return NonlinearFunction{isinplace(f, 3), FullSpecialize}(f; kwargs...)
+    return NonlinearFunction{isinplace(f, 3), DEFAULT_SPECIALIZATION}(f; kwargs...)
 end
 NonlinearFunction(f::NonlinearFunction; kwargs...) = f