Fix linting issues: canonicalheader, embeddedstructfieldcheck, iotamixing, makezero, testableexamples, wastedassign, usetesting, tparallel, unconvert, intrange, iface

- canonicalheader: fix cacheTTL header value to canonical form
- embeddedstructfieldcheck: move embedded fields before regular fields in 4 structs
- iotamixing: split const blocks mixing iota with non-iota constants
- makezero: use make([]T, 0, n) instead of make([]T, n) before appending
- testableexamples: add missing Output: comment to ExampleOption_UnwrapOrZero
- wastedassign: remove wasted initial assignments in 4 locations
- usetesting: replace os.MkdirTemp/os.Setenv with t.TempDir/t.Setenv in tests
- tparallel: add t.Parallel() to 8 top-level test functions
- unconvert: remove 16 unnecessary type conversions
- intrange: convert 3 for loops to use integer range syntax
- iface: consolidate identical EditPrompter and Prompt interfaces via type alias

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

pkg/cmd/variable/set/set.go

@@ -203,7 +203,7 @@ func setRun(opts *SetOptions) error {
 
 	var errs []error
 	cs := opts.IO.ColorScheme()
-	for i := 0; i < len(variables); i++ {
+	for range len(variables) {
 		result := <-setc
 		if result.Err != nil {
 			errs = append(errs, result.Err)

pkg/cmd/variable/set/set_test.go

@@ -477,7 +477,7 @@ func Test_getBody(t *testing.T) {
 
 func Test_getVariablesFromOptions(t *testing.T) {
 	genFile := func(s string) string {
-		f, err := os.CreateTemp("", "gh-env.*")
+		f, err := os.CreateTemp(t.TempDir(), "gh-env.*")
 		if err != nil {
 			t.Fatal(err)
 			return ""