Cache regex instances in most cases (#27699)

Using static Regex functions that take in a pattern is bad because the pattern constantly needs to be re-parsed. With https://github.com/space-wizards/RobustToolbox/pull/5107, the engine has an analyzer to warn for this practice now.

This commit brings most of content up to snuff already, though some of the tricker code I left for somebody else.

Content.Server/Speech/EntitySystems/ScrambledAccentSystem.cs

@@ -7,6 +7,8 @@ namespace Content.Server.Speech.EntitySystems
 {
     public sealed class ScrambledAccentSystem : EntitySystem
     {
+        private static readonly Regex RegexLoneI = new(@"(?<=\ )i(?=[\ \.\?]|$)");
+
         [Dependency] private readonly IRobustRandom _random = default!;
 
         public override void Initialize()
@@ -34,7 +36,7 @@ namespace Content.Server.Speech.EntitySystems
             msg = msg[0].ToString().ToUpper() + msg.Remove(0, 1);
 
             // Capitalize lone i's
-            msg = Regex.Replace(msg, @"(?<=\ )i(?=[\ \.\?]|$)", "I");
+            msg = RegexLoneI.Replace(msg, "I");
             return msg;
         }