Add real-time-safe SPSC ring buffer and denormal-aware delay line

[matt-edmondson]

Summary

Implements upstream roadmap item #3 from the .NET VST3 effects host plan: real-time-safe buffers for the audio↔UI boundary and for delay-based DSP. Both types are additive and pre-allocate their backing store so they never allocate, lock, or block on the hot path.

SpscRingBuffer<T>

A lock-free, wait-free, fixed-capacity single-producer/single-consumer ring buffer.

• Allocation-free and non-blocking TryEnqueue / TryDequeue / TryPeek — safe to call from an audio/render thread (producer) with a UI/worker thread (consumer).
• Correctness via acquire/release ordering (Volatile.Read/Volatile.Write); one reserved slot disambiguates full vs empty.
• Head/tail indices are cache-line padded (separate non-generic [StructLayout(Explicit)] struct) to avoid false sharing.
• Intended for pushing meter/scope telemetry from the audio callback to the UI thread (see plan §"Real-Time Safety").

DelayLine

A fixed-capacity circular delay line for audio-rate float samples.

• Integer (Read) and linear-interpolated (ReadInterpolated) taps; Process(input, delay) is the common write-then-tap idiom.
• Read(d) returns x[n-d] with d in [0, Capacity] (delay 0 = most recently written sample), so Process(x, D) outputs the input from exactly D samples earlier.
• Denormal-aware: subnormal magnitudes are flushed to zero on write to avoid the large CPU penalty denormals cause in decaying feedback paths.
• Power-of-two backing store for branch-free index wrapping.

Testing

Added MSTest coverage for both types (SpscRingBufferTests, DelayLineTests), including FIFO ordering, full/empty edges, wraparound, denormal flushing, interpolation, argument validation, and a 1M-item concurrent producer/consumer soak test. Full suite: 351/351 passing locally (net10.0).

Note: the local sandbox only has .NET SDK 10.0.108, which is older than the Roslyn the pinned ktsu.Sdk analyzers (2.8.0) require, so tests were run with the standard dotnet/MSTest runner against net10.0. CI runs the full multi-target build with analyzers and style enforcement.

🤖 Part of the ktsu VST plugin upstream-enablement work.

https://claude.ai/code/session_01JQ3bQMuSYuumAnQZaYUKP7

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