fix: add Julia 1.10 compatibility for Base.ispublic

Base.ispublic was introduced in Julia 1.11. This change wraps the call
in a @static if VERSION check to maintain compatibility with Julia 1.10
and earlier supported versions.

Fixes loading error on Julia 1.10:
ERROR: UndefVarError: `ispublic` not defined

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ChrisRackauckas

src/ModelingToolkit.jl

@@ -112,8 +112,11 @@ macro import_mtkbase()
         name in banned_names && continue
         startswith(string(name), '#') && continue
         push!(inner_using_expr.args, Expr(:., name))
-        if Base.ispublic(MTKBase, name) && !Base.isexported(MTKBase, name)
-            push!(inner_public_expr.args, name)
+        # Base.ispublic was added in Julia 1.11
+        @static if VERSION >= v"1.11"
+            if Base.ispublic(MTKBase, name) && !Base.isexported(MTKBase, name)
+                push!(inner_public_expr.args, name)
+            end
         end
     end