reorganize: consolidate demo directories

- Consolidate _demo, _pydemo, _embdemo into single _demo directory structure
- Organize demos by language: _demo/{go,py,c,embed}/
- Categorize demos based on imports:
- Python library demos (py imports) → _demo/py/
- C/C++ library demos (c/cpp imports) → _demo/c/
- Go-specific demos → _demo/go/
- Embedded demos → _demo/embed/
- Move C-related demos (asm*, cabi*, cgo*, linkname, targetsbuild) from go/ to c/
- Update all path references in README.md and GitHub workflows
- Improve demo organization and navigation as requested in #1256

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

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

_demo/go/reflectfunc/reflectfunc.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"fmt"
+	"reflect"
+)
+
+func add(a, b int) int {
+	return a + b
+}
+
+func main() {
+	fn := func(a, b int) int {
+		return a + b
+	}
+	var i int
+	fn1 := func() {
+		i++
+	}
+	fn2 := func() func() {
+		return func() {
+			println("closure", i)
+		}
+	}
+
+	fns := []any{add, fn, fn1, fn2}
+	for _, fn := range fns {
+		v := reflect.ValueOf(fn)
+		fmt.Println(v.Type())
+		fmt.Println(v.Kind())
+		if v.Kind() != reflect.Func {
+			panic(fmt.Sprintf("not func: %T", fn))
+		}
+
+		t := v.Type()
+		fmt.Println(t)
+		fmt.Println(t.Kind())
+		if t.Kind() != reflect.Func {
+			panic(fmt.Sprintf("not func: %T", fn))
+		}
+	}
+}