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/map.go

@@ -0,0 +1,51 @@
+package utils
+
+import "sync"
+
+type Map[K comparable, V any] struct {
+	m sync.Map
+}
+
+func NewMap[K comparable, V any]() *Map[K, V] {
+	return &Map[K, V]{
+		m: sync.Map{},
+	}
+}
+
+func (m *Map[K, V]) Delete(key K) {
+	m.m.Delete(key)
+}
+
+func (m *Map[K, V]) Load(key K) (value V, ok bool) {
+	v, ok := m.m.Load(key)
+	if !ok {
+		return value, ok
+	}
+
+	return v.(V), ok
+}
+
+func (m *Map[K, V]) LoadAndDelete(key K) (value V, loaded bool) {
+	v, loaded := m.m.LoadAndDelete(key)
+	if !loaded {
+		return value, loaded
+	}
+
+	return v.(V), loaded
+}
+
+func (m *Map[K, V]) LoadOrStore(key K, value V) (actual V, loaded bool) {
+	a, loaded := m.m.LoadOrStore(key, value)
+
+	return a.(V), loaded
+}
+
+func (m *Map[K, V]) Range(f func(key K, value V) bool) {
+	m.m.Range(func(key, value any) bool {
+		return f(key.(K), value.(V))
+	})
+}
+
+func (m *Map[K, V]) Store(key K, value V) {
+	m.m.Store(key, value)
+}