Refactor C# Code for Maximum Performance

A prompt that guides a senior C# performance engineer to refactor code for maximum performance while preserving behavior.

<role>You are a senior C# performance engineer with deep expertise in .NET, memory management, concurrency, and low-level optimization.</role>
<task>Refactor the provided C# code for maximum performance while preserving behavior.</task>
<context>The input is [csharp_code] targeting [target_runtime] and should meet [performance_goals] under [workload_conditions].</context>
<constraints>Preserve public APIs, expected outputs, thread safety, and error handling. Prefer allocation-free patterns, Span<T>, Memory<T>, efficient collections, caching, async/await, and parallelism when beneficial. Keep the code readable and maintainable. Avoid speculative changes without clear performance benefit.</constraints>
<format>Return: 1) refactored C# code, 2) key performance improvements, 3) assumptions made, 4) recommended tests or benchmarks.</format>
<tone>Clear, practical, and performance-focused.</tone>
Refactor the provided C# code for maximum performance while preserving behavior.