refactor(audience-sdk): introduce IdentityTypeExtensions.ParseLowercaseString

Adds the inverse of ToLowercaseString so callers reading user-supplied or wire-format identity
strings can round-trip back into the enum without hand-rolling another switch.

- IdentityType.cs: adds IdentityTypeExtensions.ParseLowercaseString, the case-insensitive inverse of
  ToLowercaseString. Falls back to Custom for unknown / empty values; never throws.
- AudienceSample.cs: ParseIdentityType reverse mapper delegates to
  IdentityTypeExtensions.ParseLowercaseString instead of hand-rolling its own switch.

Author: ImmutableJeffrey

examples/audience/Assets/SampleApp/Scripts/AudienceSample.cs

@@ -375,16 +375,7 @@ private void ResetIdentityMirror()
         // Parses a wire-format identity string (e.g. "steam") back into the
         // IdentityType enum the SDK now requires. Falls back to Custom for
         // unknown or empty values.
-        private static IdentityType ParseIdentityType(string? value) => (value ?? "").ToLowerInvariant() switch
-        {
-            "passport" => IdentityType.Passport,
-            "steam"    => IdentityType.Steam,
-            "epic"     => IdentityType.Epic,
-            "google"   => IdentityType.Google,
-            "apple"    => IdentityType.Apple,
-            "discord"  => IdentityType.Discord,
-            "email"    => IdentityType.Email,
-            _          => IdentityType.Custom,
-        };
+        private static IdentityType ParseIdentityType(string? value) =>
+            IdentityTypeExtensions.ParseLowercaseString(value);
     }
 }

src/Packages/Audience/Runtime/IdentityType.cs

@@ -56,5 +56,18 @@ internal static class IdentityTypeExtensions
             _ => throw new System.ArgumentOutOfRangeException(nameof(type), type,
                 "Unknown IdentityType value; cast an out-of-range value."),
         };
+
+        internal static IdentityType ParseLowercaseString(string? value) =>
+            (value ?? string.Empty).ToLowerInvariant() switch
+            {
+                "passport" => IdentityType.Passport,
+                "steam" => IdentityType.Steam,
+                "epic" => IdentityType.Epic,
+                "google" => IdentityType.Google,
+                "apple" => IdentityType.Apple,
+                "discord" => IdentityType.Discord,
+                "email" => IdentityType.Email,
+                _ => IdentityType.Custom,
+            };
     }
 }