Refactor Core Architecture and Transition to v2.0.0.

[brunoga]

Overview
This PR represents a major evolution of the deep library. It focuses on modularizing the internal implementation, significantly improving performance and memory efficiency, and unifying the public API into a more ergonomic and consistent model. Due to breaking changes in the Condition interface and function signatures, this PR transitions the project to v2.0.0.

Key Changes

1. Modular Architecture

• Deconstructed the monolithic patch.go and condition.go into specialized logical units (_ops, _parser, _serialization, _utils).
• Improved maintainability and isolated testing for core components.

2. Unified & Ergonomic API

• Polymorphic Options: Introduced an interface-based options pattern. A single deep.IgnorePath("path") now works seamlessly for both Copy and Diff.
• Blind Updates: Added Node.Put(value) to the Builder, allowing for "blind" sets that bypass strict consistency checks—ideal for API-driven updates.
• Navigation: Exported Node.Navigate(path) supporting both Go-style notation and JSON Pointers.
• Deprecation: CopySkipUnsupported is now deprecated in favor of the deep.SkipUnsupported() option.

3. High-Performance Optimizations

• Copy Fast-Path: Achieved up to 7x faster cloning for basic types by bypassing the recursive engine when no options are present.
• Reduced Allocations:
  • Implemented sync.Pool for internal pointer tracking maps.
  • Lazy path construction: Structural paths are now only computed if IgnorePath options are active.
• Reflection Reduction: Refactored condition evaluation to use a "sealed" internal interface instead of MethodByName reflection, significantly speeding up ApplyChecked calls.
• Slice Diffing: Added $O(N)$ fast-paths for simple appends and removals.

4. Robustness & Bug Fixes

• Fixed a critical bug in Copy where self-referencing value-type structs were not correctly detected as cycles.
• Added guards against panics when handling nil interfaces or nil pointers implementing the Copier interface.

5. Documentation & Standards

• Completely restructured README.md to follow a logical progression (Quick Start → Core Concepts → Advanced Logic).
• Added 100% Go doc coverage for the public interface.
• Updated module path to github.com/brunoga/deep/v2 per Go SemVer requirements.