Prettify NaN/Infinity in DebugStringConvertible

Summary:
Improve readability of debug output by rendering floating-point NaN and Infinity as "NaN", "Infinity", and "-Infinity" instead of the lowercase stream defaults. This aligns React Native debug strings with developer expectations and JS conventions, making logs and snapshots clearer.

Changelog: [Internal]

---
AI generated Summary & Test Plan from DEV97500299

Differential Revision: D95499647

Author: NickGerleman

packages/react-native/Libraries/Components/Pressable/__tests__/Pressable-itest.js

@@ -148,8 +148,8 @@ describe('<Pressable>', () => {
             <rn-paragraph
               allowFontScaling="true"
               ellipsizeMode="tail"
-              fontSize="nan"
-              fontSizeMultiplier="nan"
+              fontSize="NaN"
+              fontSizeMultiplier="NaN"
               foregroundColor="rgba(0, 0, 0, 0)"
               overflow="hidden">
               the quick brown fox

packages/react-native/Libraries/Text/__tests__/Text-itest.js

@@ -40,8 +40,8 @@ describe('<Text>', () => {
           <rn-paragraph
             allowFontScaling="true"
             ellipsizeMode="tail"
-            fontSize="nan"
-            fontSizeMultiplier="nan"
+            fontSize="NaN"
+            fontSizeMultiplier="NaN"
             foregroundColor="rgba(0, 0, 0, 0)"
             overflow="hidden">
             {TEST_TEXT}

packages/react-native/ReactCommon/react/renderer/debug/DebugStringConvertible.cpp

@@ -7,6 +7,7 @@
 
 #include "DebugStringConvertible.h"
 
+#include <cmath>
 #include <cstdint>
 #include <iomanip>
 #include <sstream>
@@ -127,6 +128,14 @@ SharedDebugStringConvertibleList DebugStringConvertible::getDebugProps() const {
  * `toString`-family implementation.
  */
 std::string toString(const double& value) {
+  // Handle special floating-point values with prettier output
+  if (std::isnan(value)) {
+    return "NaN";
+  }
+  if (std::isinf(value)) {
+    return value < 0 ? "-Infinity" : "Infinity";
+  }
+
   std::ostringstream stream;
   stream << std::fixed << std::setprecision(4) << value;
   std::string result = stream.str();