refactor: introduce constants for improved maintainability in tests and server configurations

- Added constants for test endpoints, usernames, and XML headers in client_test.go and device_certificates_test.go to enhance readability and reduce hardcoded values.
- Updated various test cases to utilize these constants, ensuring consistency across tests.
- Refactored imaging settings and server configurations to use defined constants for default values, improving clarity and maintainability in server/device.go and server/imaging.go.
- Enhanced comments throughout the code to clarify functionality and adhere to best practices.

discovery/discovery.go

@@ -94,6 +94,8 @@ func Discover(ctx context.Context, timeout time.Duration) ([]*Device, error) {
 }
 
 // DiscoverWithOptions discovers ONVIF devices with custom options.
+//
+//nolint:gocyclo // Discovery function has high complexity due to multiple network operations
 func DiscoverWithOptions(ctx context.Context, timeout time.Duration, opts *DiscoverOptions) ([]*Device, error) {
 	if opts == nil {
 		opts = &DiscoverOptions{}
@@ -236,7 +238,7 @@ func generateUUID() string {
 
 // resolveNetworkInterface resolves a network interface by name or IP address.
 //
-//nolint:gocognit // Network interface resolution has high complexity due to multiple validation paths
+//nolint:gocyclo,gocognit // Network interface resolution has high complexity due to multiple validation paths
 func resolveNetworkInterface(ifaceSpec string) (*net.Interface, error) {
 	// Try to get interface by name (e.g., "eth0", "wlan0")
 	if iface, err := net.InterfaceByName(ifaceSpec); err == nil {