Unify undefined labels and JSON guards

Adds a shared `common::kUndefined` string and replaces scattered literal "Undefined" fallbacks across DMX, RDM, LTC, and MIDI-related code. The remote config JSON endpoints now enforce non-null/non-zero output buffers with assertions, and several small consistency cleanups were applied (macro style `#ifdef`, Art-Net node ID print usage, and minor formatting/log message tidy-ups).

Author: vanvught

common/include/common/utils/utils_string.h

@@ -33,6 +33,7 @@ inline constexpr char kWarning[] = "Warning";
 inline constexpr char kError[] = "Error";
 inline constexpr char kSuccess[] = "Success";
 inline constexpr char kUnknown[] = "Unknown"; 
+inline constexpr char kUndefined[] = "Undefined";
 
 constexpr const char* IsSuccess(bool is_success) {
   return is_success ? kSuccess : kError;

lib-network/src/core/network_memory.h

@@ -87,7 +87,7 @@ class Allocator {
 
     uint8_t* Allocate() {
         if (IsFull()) {
-            ERROR("Allocate:Full!");
+            ERROR("Full");
             return nullptr;
         }
 
@@ -105,7 +105,7 @@ class Allocator {
         assert(size <= kBlockSize);
 
         if (IsFull()) {
-            ERROR("Allocate:Full!");
+            ERROR("Full");
             return UINT16_MAX;
         }