feat(client): add functional option pattern for JWT auth config

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/slurm/options_test.go

@@ -0,0 +1,154 @@
+package slurm
+
+import (
+	"crypto/rand"
+	"net/http"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestNewClientWithOpts_JWTKey_Success(t *testing.T) {
+	key := make([]byte, 32)
+	if _, err := rand.Read(key); err != nil {
+		t.Fatalf("generate key: %v", err)
+	}
+	dir := t.TempDir()
+	keyPath := filepath.Join(dir, "jwt.key")
+	if err := os.WriteFile(keyPath, key, 0600); err != nil {
+		t.Fatalf("write key file: %v", err)
+	}
+
+	client, err := NewClientWithOpts("http://localhost:6820/",
+		WithJWTKey(keyPath),
+		WithUsername("testuser"),
+	)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if client == nil {
+		t.Fatal("expected non-nil client")
+	}
+
+	transport, ok := client.client.Transport.(*JWTAuthTransport)
+	if !ok {
+		t.Fatalf("expected *JWTAuthTransport, got %T", client.client.Transport)
+	}
+	if transport.UserName != "testuser" {
+		t.Errorf("expected username %q, got %q", "testuser", transport.UserName)
+	}
+}
+
+func TestNewClientWithOpts_InvalidKeyPath_Error(t *testing.T) {
+	client, err := NewClientWithOpts("http://localhost:6820/",
+		WithJWTKey("/nonexistent/key"),
+		WithUsername("testuser"),
+	)
+	if err == nil {
+		t.Fatal("expected error for invalid key path, got nil")
+	}
+	if client != nil {
+		t.Fatal("expected nil client on error")
+	}
+}
+
+func TestNewClientWithOpts_BackwardCompatible(t *testing.T) {
+	client, err := NewClientWithOpts("http://localhost:6820/")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if client == nil {
+		t.Fatal("expected non-nil client")
+	}
+	if client.client != http.DefaultClient {
+		t.Error("expected http.DefaultClient when no options provided")
+	}
+}
+
+func TestNewClientWithOpts_AllServicesInitialized(t *testing.T) {
+	client, err := NewClientWithOpts("http://localhost:6820/")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	services := []struct {
+		name string
+		svc  interface{}
+	}{
+		{"Jobs", client.Jobs},
+		{"Nodes", client.Nodes},
+		{"Partitions", client.Partitions},
+		{"Reservations", client.Reservations},
+		{"Diag", client.Diag},
+		{"Ping", client.Ping},
+		{"Licenses", client.Licenses},
+		{"Reconfigure", client.Reconfigure},
+		{"Shares", client.Shares},
+		{"SlurmdbDiag", client.SlurmdbDiag},
+		{"SlurmdbConfig", client.SlurmdbConfig},
+		{"SlurmdbTres", client.SlurmdbTres},
+		{"SlurmdbQos", client.SlurmdbQos},
+		{"SlurmdbAssocs", client.SlurmdbAssocs},
+		{"SlurmdbInstances", client.SlurmdbInstances},
+		{"SlurmdbUsers", client.SlurmdbUsers},
+		{"SlurmdbClusters", client.SlurmdbClusters},
+		{"SlurmdbWckeys", client.SlurmdbWckeys},
+		{"SlurmdbAccounts", client.SlurmdbAccounts},
+		{"SlurmdbJobs", client.SlurmdbJobs},
+	}
+
+	for _, s := range services {
+		if s.svc == nil {
+			t.Errorf("%s service is nil", s.name)
+		}
+	}
+}
+
+func TestWithTokenTTL_Custom(t *testing.T) {
+	key := make([]byte, 32)
+	if _, err := rand.Read(key); err != nil {
+		t.Fatalf("generate key: %v", err)
+	}
+	dir := t.TempDir()
+	keyPath := filepath.Join(dir, "jwt.key")
+	if err := os.WriteFile(keyPath, key, 0600); err != nil {
+		t.Fatalf("write key file: %v", err)
+	}
+
+	client, err := NewClientWithOpts("http://localhost:6820/",
+		WithJWTKey(keyPath),
+		WithUsername("testuser"),
+		WithTokenTTL(1*time.Hour),
+	)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if client == nil {
+		t.Fatal("expected non-nil client")
+	}
+}
+
+func TestWithTokenLeeway_Custom(t *testing.T) {
+	key := make([]byte, 32)
+	if _, err := rand.Read(key); err != nil {
+		t.Fatalf("generate key: %v", err)
+	}
+	dir := t.TempDir()
+	keyPath := filepath.Join(dir, "jwt.key")
+	if err := os.WriteFile(keyPath, key, 0600); err != nil {
+		t.Fatalf("write key file: %v", err)
+	}
+
+	client, err := NewClientWithOpts("http://localhost:6820/",
+		WithJWTKey(keyPath),
+		WithUsername("testuser"),
+		WithTokenLeeway(1*time.Minute),
+	)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if client == nil {
+		t.Fatal("expected non-nil client")
+	}
+}