Refactor node rendering, serialization, and graph model architecture

[imakris]

Type of change

• New feature
• Breaking change
• Documentation/refactoring

Description

This is a comprehensive refactoring that improves the architecture and rendering pipeline of the node editor:

Major Changes

Node Rendering System

• Introduced NodeRenderingUtils with centralized node rendering constants and utilities
• Implemented shadow atlas generation with multi-pass box blur for improved visual quality
• Added DefaultNodeGeometryBase to consolidate shared geometry logic between horizontal and vertical layouts
• Enhanced DefaultNodePainter with sophisticated shadow rendering and caching

Graph Model Architecture

• Introduced ConnectionIdIndex for efficient connection lookups by node and port
• Changed allNodeIds() return type from std::unordered_set<NodeId> to NodeIdSet const & for better performance (avoids copies)
• Updated DataFlowGraphModel to use the new index-based connection tracking
• Refactored serialization validation into dedicated SerializationValidation module with reusable utilities

Scene and Graphics

• Split BasicGraphicsScene functionality: moved group-related methods to new BasicGraphicsSceneGroups.cpp
• Enhanced GraphicsView with smooth zoom animation support and improved cache management
• Improved ConnectionGraphicsObject with cached geometry rebuilding and better bounding rect calculations
• Updated NodeGraphicsObject with rendering optimizations and graphics view integration

Serialization & Validation

• Created SerializationValidation.hpp/cpp with robust JSON parsing utilities
• Centralized node/group/connection ID parsing with proper error handling
• Improved validation of serialized graph data with detailed error messages
• Removed duplicate parsing logic across multiple files

Code Quality

• Removed obsolete PySide2/Shiboken CMake modules
• Cleaned up unused includes and forward declarations
• Improved const-correctness and reference semantics
• Added comprehensive namespace organization with anonymous namespaces for internal helpers

Breaking Changes

1. AbstractGraphModel::allNodeIds() now returns NodeIdSet const & instead of std::unordered_set<NodeId>. This requires graph model implementations to maintain a member variable instead of computing the set on-the-fly.

2. Connection tracking now uses ConnectionIdIndex internally. Custom graph models should leverage this for efficient connection queries.

3. Serialization functions moved to SerializationValidation namespace. Code using jsonValueToNodeId() or similar functions should use the new detail::read_node_id() utilities.

Migration Guide

For custom graph models:

// Before
std::unordered_set<NodeId> allNodeIds() const override {
    std::unordered_set<NodeId> result;
    for (auto& p : _models) result.insert(p.first);
    return result;
}

// After
AbstractGraphModel::NodeIdSet const &allNodeIds() const override {
    return _nodeIds;  // Maintain as member variable
}

Testing

• Qt version tested: 5.15+
• Existing tests still pass
• Added tests for zoom animation features
• Serialization validation tests included

Related issue

Improves overall architecture and rendering performance of the node editor library.

https://claude.ai/code/session_01PgU81XZwKqXaPr628mVdQj