chore: refactor time.Duration -> int64 milliseconds for FE consumption (#1944)

* Changes all public-facing codersdk types to use a plain int64 (milliseconds) instead of time.Duration.
* Makes autostart_schedule a *string as it may not be present.
* Adds a utils/ptr package with some useful methods.

coderd/util/ptr/ptr_test.go

@@ -0,0 +1,81 @@
+package ptr_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/coder/coder/coderd/util/ptr"
+)
+
+func Test_Ref_Deref(t *testing.T) {
+	t.Parallel()
+
+	t.Run("String", func(t *testing.T) {
+		t.Parallel()
+		val := "test"
+		p := ptr.Ref(val)
+		assert.Equal(t, &val, p)
+	})
+
+	t.Run("Bool", func(t *testing.T) {
+		t.Parallel()
+		val := true
+		p := ptr.Ref(val)
+		assert.Equal(t, &val, p)
+	})
+
+	t.Run("Int64", func(t *testing.T) {
+		t.Parallel()
+		val := int64(42)
+		p := ptr.Ref(val)
+		assert.Equal(t, &val, p)
+	})
+
+	t.Run("Float64", func(t *testing.T) {
+		t.Parallel()
+		val := float64(3.14159)
+		p := ptr.Ref(val)
+		assert.Equal(t, &val, p)
+	})
+}
+
+func Test_NilOrEmpty(t *testing.T) {
+	t.Parallel()
+	nilString := (*string)(nil)
+	emptyString := ""
+	nonEmptyString := "hi"
+
+	assert.True(t, ptr.NilOrEmpty(nilString))
+	assert.True(t, ptr.NilOrEmpty(&emptyString))
+	assert.False(t, ptr.NilOrEmpty(&nonEmptyString))
+}
+
+func Test_NilOrZero(t *testing.T) {
+	t.Parallel()
+
+	nilInt64 := (*int64)(nil)
+	nilFloat64 := (*float64)(nil)
+	nilDuration := (*time.Duration)(nil)
+
+	zeroInt64 := int64(0)
+	zeroFloat64 := float64(0.0)
+	zeroDuration := time.Duration(0)
+
+	nonZeroInt64 := int64(1)
+	nonZeroFloat64 := float64(3.14159)
+	nonZeroDuration := time.Hour
+
+	assert.True(t, ptr.NilOrZero(nilInt64))
+	assert.True(t, ptr.NilOrZero(nilFloat64))
+	assert.True(t, ptr.NilOrZero(nilDuration))
+
+	assert.True(t, ptr.NilOrZero(&zeroInt64))
+	assert.True(t, ptr.NilOrZero(&zeroFloat64))
+	assert.True(t, ptr.NilOrZero(&zeroDuration))
+
+	assert.False(t, ptr.NilOrZero(&nonZeroInt64))
+	assert.False(t, ptr.NilOrZero(&nonZeroFloat64))
+	assert.False(t, ptr.NilOrZero(&nonZeroDuration))
+}