test: move export test to CI folder

- Moved export test from _demo/embedded/export_test/ to test/export_test.go
- Converted shell-based test to Go test for better CI integration
- Test verifies that //export directive correctly exports functions with different symbol names
- Fixed test to use repository version of llgo instead of system-installed version

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

_demo/embedded/export_test/main.go

@@ -1,22 +0,0 @@
-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))
-}

_demo/embedded/export_test/test.sh

@@ -1,43 +0,0 @@
-#!/bin/bash
-set -e
-
-echo "Testing //export with different symbol names..."
-
-# Set LLGO_ROOT to repository root
-export LLGO_ROOT=/workspace
-
-# Build the test program
-echo "Building test program..."
-/workspace/llgo build -o test_export main.go || exit 1
-
-# Check for expected symbols using nm
-echo "Verifying symbols with nm..."
-
-# Should find LPSPI2_IRQHandler (not interruptLPSPI2)
-if nm test_export | grep -q "T LPSPI2_IRQHandler"; then
-    echo "✓ Symbol LPSPI2_IRQHandler found"
-else
-    echo "✗ Symbol LPSPI2_IRQHandler not found"
-    echo "Available symbols:"
-    nm test_export | grep " T "
-    exit 1
-fi
-
-# Should find SysTick_Handler (not systemTickHandler)
-if nm test_export | grep -q "T SysTick_Handler"; then
-    echo "✓ Symbol SysTick_Handler found"
-else
-    echo "✗ Symbol SysTick_Handler not found"
-    exit 1
-fi
-
-# Should find Add (same name)
-if nm test_export | grep -q "T Add"; then
-    echo "✓ Symbol Add found"
-else
-    echo "✗ Symbol Add not found"
-    exit 1
-fi
-
-echo ""
-echo "All symbol checks passed! ✓"