Investigate and Implement AES with Zero Allocation

[MrMatthewLayton]

A community member has requested support for zero-allocation AES encryption/decryption. This would improve performance by reducing memory allocations, especially in high-throughput or constrained environments.

Tasks

• Investigate current .NET capabilities for zero-allocation cryptography.
• Implement AES functionality that avoids allocations where possible.
• Add benchmarks to compare performance with current AES implementation.
• Document any potentially limiting factors.

Acceptance Criteria

• AES encryption/decryption can be performed using Span<byte> without heap allocations.
• Tests verify functional correctness and zero-allocation behavior.
• Benchmarks show improved memory efficiency.