feat: Complete target system with C# bindings and resource inference (#458)

* feat: Add Schema Registry and Validation Framework

This commit introduces a comprehensive schema registry and validation framework, providing schema-based validation of resources and policy effects.

- Thread-safe, in-memory registry for schema storage and management
- Global registry patterns for effects and resources
- Concurrent access with proper error handling
- Unicode schema names support

- JSON Schema-compliant validation for all primitive types
- Advanced constraint validation (patterns, ranges, length limits)
- Discriminated union support with anyOf schemas
- Detailed error reporting with nested validation paths
- Discriminated subobject validation for polymorphic schemas

- **Registry Tests**: All registry operations
- **Effect Tests**: Policy effect validation
- **Resource Tests**: Resource validation
- **Validation Tests**: Core validation engine
- Thread-safety, error handling, integration scenarios, edge cases

- **Dependencies**: dashmap, once_cell, regex
- **Thread Safety**: Minimal locking with Rc<Schema> sharing
- **Error Types**: TypeMismatch, OutOfRange, PatternMismatch, etc.

- Complete schema registry and validation subsystem
- Comprehensive test coverage
- Foundation for policy validation in Regorus

Benchmarks:

- Criterion benchmarks for basic types, effects and Azure resources
- Performance range: 3.22ns (string) to 34.74µs (Azure VM resource schema validation)
- String withs patterns validation: 30.2µs. Need to explore whether regex caching helps
  bring this down.
- Azure policy effects: 188ns-1.4µs

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* feat: Complete target system with C# bindings and resource inference

- Add comprehensive target system with TargetRegistry and target-aware compilation
- Implement resource type inference from policy equality expressions
- Create modular C# bindings with separate wrapper classes for each concept
- Add thread-safe CompiledPolicy with reference counting for safe disposal
- Enhance FFI with detailed error propagation and target functionality
- Create TargetExampleApp demonstrating Azure Policy integration
- Add CI/CD pipeline testing for all C# applications
- Support target definitions with schema validation and resource selectors
- Implement PolicyModule struct and target-aware compilation methods
- Add comprehensive test coverage for target functionality

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

---------

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/csharp/Regorus/Regorus.csproj

@@ -13,6 +13,10 @@
         <PackageReadmeFile>README.md</PackageReadmeFile>
     </PropertyGroup>
 
+    <ItemGroup>
+        <PackageReference Include="System.Text.Json" Version="8.0.0" />
+    </ItemGroup>
+
     <!--
         $(RegorusFFIArtifactsDir) is the location where regorus shared libraries have been
         built for various platforms and copied to. RegorusFFIArtifactsDir is passed in
@@ -20,8 +24,10 @@
 
         For each target triple, `Pack` expects the regorus ffi shared library
         to be found in $(RegorusFFIArtifactsDir)/<target-triple>/release.
+
+        If $(IgnoreMissingArtifacts) is not set, ensure that the binaries for officially supported platforms exists.
     -->
-    <Target Name="ChecksRegorusFFIArtifactsDir" BeforeTargets="Pack">
+    <Target Name="ChecksRegorusFFIArtifactsDir" BeforeTargets="Pack" Condition="'$(IgnoreMissingArtifacts)' == ''">
         <Error Text="RegorusFFIArtifactsDir must be supplied." Condition="$(RegorusFFIArtifactsDir) == ''" />
 
         <!-- Ensure that the binaries for officially supported platforms exists. -->