Optimize StringDehumanizeExtensions by caching compiled regexes

This change replaces inline, uncompiled regexes in ToPascalCase and ToSnakeCase with static readonly fields configured with RegexOptions.Compiled and RegexOptions.CultureInvariant. This avoids the overhead of parsing and compiling the patterns on every call, leading to better performance and fewer allocations.

- Added static readonly Regex fields for all patterns.
- Updated methods to use the cached instances.
- Added RegexOptions.CultureInvariant for consistency with the class's goal.
- Added a blank line before the return statement in ToCamelCase to follow style guidelines.

Author: google-labs-jules[bot]

osu.Game/Extensions/StringDehumanizeExtensions.cs

@@ -36,6 +36,11 @@ namespace osu.Game.Extensions
     /// </summary>
     public static class StringDehumanizeExtensions
     {
+        private static readonly Regex pascal_case_regex = new Regex(@"(?:^|_|-| +)(.)", RegexOptions.Compiled | RegexOptions.CultureInvariant);
+        private static readonly Regex snake_case_step1_regex = new Regex(@"([\p{Lu}]+)([\p{Lu}][\p{Ll}])", RegexOptions.Compiled | RegexOptions.CultureInvariant);
+        private static readonly Regex snake_case_step2_regex = new Regex(@"([\p{Ll}\d])([\p{Lu}])", RegexOptions.Compiled | RegexOptions.CultureInvariant);
+        private static readonly Regex snake_case_step3_regex = new Regex(@"[-\s]", RegexOptions.Compiled | RegexOptions.CultureInvariant);
+
         /// <summary>
         /// Converts the string to "Pascal case" (also known as "upper camel case").
         /// </summary>
@@ -46,7 +51,7 @@ public static class StringDehumanizeExtensions
         /// </example>
         public static string ToPascalCase(this string input)
         {
-            return Regex.Replace(input, "(?:^|_|-| +)(.)", match => match.Groups[1].Value.ToUpperInvariant());
+            return pascal_case_regex.Replace(input, match => match.Groups[1].Value.ToUpperInvariant());
         }
 
         /// <summary>
@@ -60,6 +65,7 @@ public static string ToPascalCase(this string input)
         public static string ToCamelCase(this string input)
         {
             string word = input.ToPascalCase();
+
             return word.Length > 0 ? char.ToLowerInvariant(word[0]) + word.Substring(1) : word;
         }
 
@@ -73,9 +79,9 @@ public static string ToCamelCase(this string input)
         /// </example>
         public static string ToSnakeCase(this string input)
         {
-            return Regex.Replace(
-                Regex.Replace(
-                    Regex.Replace(input, @"([\p{Lu}]+)([\p{Lu}][\p{Ll}])", "$1_$2"), @"([\p{Ll}\d])([\p{Lu}])", "$1_$2"), @"[-\s]", "_").ToLowerInvariant();
+            return snake_case_step3_regex.Replace(
+                snake_case_step2_regex.Replace(
+                    snake_case_step1_regex.Replace(input, "$1_$2"), "$1_$2"), "_").ToLowerInvariant();
         }
 
         /// <summary>