major: Overhaul functionality, tests, benchmarks, docs

[DecSmith42]

No description provided.

[Copilot]

Pull Request Overview

This pull request implements a major overhaul of the DecSm.Extensions.Json library, focusing on refactoring the API structure, improving functionality, and enhancing the build and test infrastructure.

• Replaced single JsonUtil class with modular JsonExtensions partial classes organized by functionality
• Added comprehensive benchmark project for performance testing
• Updated library to target multiple .NET frameworks (8.0, 9.0, 10.0) with enhanced documentation

Reviewed Changes

Copilot reviewed 30 out of 32 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
JsonExtensions.*.cs	New modular API structure replacing JsonUtil with specialized extension methods
DecSm.Extensions.Json.Benchmarks/	Added comprehensive performance benchmarking project
_atom/Build.cs	Updated build definition with new targets and consolidated interface implementations
README.md	Completely rewritten with clearer examples and improved documentation
*.csproj	Updated target frameworks and package references across projects

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