feat: add export symbol name test to CI for embedded targets

- Created _demo/embed/export/ with test for //export directive
- Test verifies symbols are exported with correct names (LPSPI2_IRQHandler, SysTick_Handler)
- Added CI workflow step to run the test
- Essential for embedded development where hardware requires specific symbol names

🤖 Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <51194195+luoliwoshang@users.noreply.github.com>

_demo/embed/export/main.go

@@ -0,0 +1,22 @@
+package main
+
+//export LPSPI2_IRQHandler
+func interruptLPSPI2() {
+	println("LPSPI2 interrupt handled")
+}
+
+//export SysTick_Handler
+func systemTickHandler() {
+	println("System tick")
+}
+
+//export Add
+func Add(a, b int) int {
+	return a + b
+}
+
+func main() {
+	interruptLPSPI2()
+	systemTickHandler()
+	println("Add(2, 3) =", Add(2, 3))
+}