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>

internal/codespaces/connection/connection.go

@@ -19,6 +19,7 @@ const (
 
 type TunnelClient struct {
 	*tunnels.Client
+
 	connected bool
 	mu        sync.Mutex
 }

internal/codespaces/connection/tunnels_api_server_mock.go

@@ -264,9 +264,9 @@ func newMockrelayServer(opts ...relayServerOption) (*relayServer, error) {
 		return nil, fmt.Errorf("failed to parse private key: %w", err)
 	}
 
-	server.sshConfig.AddHostKey(ssh.Signer(sshPrivateKey))
+	server.sshConfig.AddHostKey(sshPrivateKey)
 
-	server.httpServer = httptest.NewServer(http.HandlerFunc(makeConnection(server)))
+	server.httpServer = httptest.NewServer(makeConnection(server))
 
 	for _, opt := range opts {
 		opt(server)