Port envd from e2b with internalized shared packages and Connect RPC

- Copy envd source from e2b-dev/infra, internalize shared dependencies
  into envd/internal/shared/ (keys, filesystem, id, smap, utils)
- Switch from gRPC to Connect RPC for all envd services
- Update module paths to git.omukk.dev/wrenn/{sandbox,sandbox/envd}
- Add proto specs (process, filesystem) with buf-based code generation
- Implement full envd: process exec, filesystem ops, port forwarding,
  cgroup management, MMDS integration, and HTTP API
- Update main module dependencies (firecracker SDK, pgx, goose, etc.)
- Remove placeholder .gitkeep files replaced by real implementations

envd/internal/utils/atomic_test.go

@@ -0,0 +1,76 @@
+package utils
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAtomicMax_NewAtomicMax(t *testing.T) {
+	t.Parallel()
+	am := NewAtomicMax()
+	require.NotNil(t, am)
+	require.Equal(t, int64(0), am.val)
+}
+
+func TestAtomicMax_SetToGreater_InitialValue(t *testing.T) {
+	t.Parallel()
+	am := NewAtomicMax()
+
+	// Should succeed when newValue > current
+	assert.True(t, am.SetToGreater(10))
+	assert.Equal(t, int64(10), am.val)
+}
+
+func TestAtomicMax_SetToGreater_EqualValue(t *testing.T) {
+	t.Parallel()
+	am := NewAtomicMax()
+	am.val = 10
+
+	// Should succeed when newValue > current
+	assert.True(t, am.SetToGreater(20))
+	assert.Equal(t, int64(20), am.val)
+}
+
+func TestAtomicMax_SetToGreater_GreaterValue(t *testing.T) {
+	t.Parallel()
+	am := NewAtomicMax()
+	am.val = 10
+
+	// Should fail when newValue < current, keeping the max value
+	assert.False(t, am.SetToGreater(5))
+	assert.Equal(t, int64(10), am.val)
+}
+
+func TestAtomicMax_SetToGreater_NegativeValues(t *testing.T) {
+	t.Parallel()
+	am := NewAtomicMax()
+	am.val = -5
+
+	assert.True(t, am.SetToGreater(-2))
+	assert.Equal(t, int64(-2), am.val)
+}
+
+func TestAtomicMax_SetToGreater_Concurrent(t *testing.T) {
+	t.Parallel()
+	am := NewAtomicMax()
+	var wg sync.WaitGroup
+
+	// Run 100 goroutines trying to update the value concurrently
+	numGoroutines := 100
+	wg.Add(numGoroutines)
+
+	for i := range numGoroutines {
+		go func(val int64) {
+			defer wg.Done()
+			am.SetToGreater(val)
+		}(int64(i))
+	}
+
+	wg.Wait()
+
+	// The final value should be 99 (the maximum value)
+	assert.Equal(t, int64(99), am.val)
+}