feat(mutators): initial implementation of full mutation engine framework

- Added core mutation engine (`MutationEngine`) with:
  - Single and batch mutation execution (`ExecuteAsync`, `ExecuteBatchAsync`)
  - Policy evaluation and enforcement
  - Audit logging and history storage
  - Metrics collection (scoped and aggregated)
  - Interceptor pipeline for before/after/failure events

- Implemented supporting components:
  - `MutationExecutor` for low-level mutation execution
  - `PolicyRegistry` for thread-safe policy management
  - `MetricsCollectorImpl` and `MetricsScope` for in-memory metric tracking
  - Logging interceptors: `LoggingInterceptor`, `MutationHistoryLogger`, `MutationResultLogger`

- Added DI integration via `MutatorsServiceCollectionExtensions.AddMutators`:
  - Registers engine, executor, registry, auditor, history store, metrics collector
  - Optional default console logging interceptor
  - Supports engine options (`MutationEngineOptions`) and scoped configuration

- Included example usage and documentation:
  - Quick start, core concepts, best practices
  - API reference, metrics & logging, ADR references
- Exception handling improvements:
  - `MutationException` constructors made public

Author: rian-be

ModularityKit.Mutator/Abstractions/Exceptions/MutationException.cs

@@ -29,7 +29,7 @@ public class MutationException : Exception
     /// Initializes a new instance of <see cref="MutationException"/> with a specified message.
     /// </summary>
     /// <param name="message">Human-readable description of the error.</param>
-    protected MutationException(string message)
+    public MutationException(string message)
         : base(message)
     {
     }
@@ -40,7 +40,7 @@ protected MutationException(string message)
     /// </summary>
     /// <param name="message">Human-readable description of the error.</param>
     /// <param name="innerException">The underlying exception that triggered this error.</param>
-    protected MutationException(string message, Exception innerException)
+    public MutationException(string message, Exception innerException)
         : base(message, innerException)
     {
     }

ModularityKit.Mutator/ModularityKit.Mutator.csproj

@@ -6,4 +6,8 @@
         <Nullable>enable</Nullable>
     </PropertyGroup>
 
+    <ItemGroup>
+      <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.2" />
+    </ItemGroup>
+
 </Project>