Add empty constructors to structs with resource fields

This change adds empty __init() {} constructors to DirectPathTextures and
IndirectPathTextures structs to fix compilation errors with recent versions
of the Slang shader compiler.

Slang versions (2025.23+) introduced stricter validation (error 41024)
that prevents default-initialization of structs containing resource types.

Changes:
- Added __init() {} to DirectPathTextures struct
- Added __init() {} to IndirectPathTextures struct

The empty constructors allow these structs to be instantiated without attempting
to default-initialize their resource fields. The existing code pattern of declaring
the struct and then assigning individual fields continues to work correctly.

Author: jvepsalainen-nv

src/dxvk/shaders/rtx/algorithm/path_state.slangh

@@ -514,6 +514,8 @@ struct PathState : IBasePayloadState
 
 struct DirectPathTextures
 {
+  __init() {} // Empty constructor is required by Slang to avoid the error 41024
+
   RWTexture2D<uint16_t> SharedFlags;
   RWTexture2D<uint16_t> SharedMediumMaterialIndex;
   RWTexture2D<float4> PrimaryDirectDiffuseLobeRadianceHitDistance;
@@ -528,6 +530,8 @@ struct DirectPathTextures
 
 struct IndirectPathTextures
 {
+  __init() {} // Empty constructor is required by Slang to avoid the error 41024
+
   Texture2D<float4> PrimaryWorldPositionWorldTriangleNormal;
   RWTexture2D<float4> IndirectRadianceHitDistance;
 };