SIMD Refactor: Merge simd-dev into dev (#55)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: aider (openrouter/anthropic/claude-sonnet-4) <aider@aider.chat>
Co-authored-by: Warp <agent@warp.dev>

lib/feeds/IFeed.md

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+# IFeed Interface
+
+`IFeed` defines the standard contract for all data feeds in QuanTAlib, ensuring consistent behavior across different data sources (synthetic, file-based, or live API).
+
+## Key Concepts
+
+* **Bidirectional Control**: The `Next(ref bool isNew)` method allows the consumer to request a new bar (`isNew = true`) or an update to the current bar (`isNew = false`).
+* **Streaming**: Designed for bar-by-bar processing, simulating real-time data flow.
+* **Batching**: Supports fetching historical data ranges via `Fetch()`.
+
+## Interface Definition
+
+```csharp
+public interface IFeed
+{
+    /// <summary>
+    /// Gets the next bar with full control over new/update state.
+    /// </summary>
+    TBar Next(ref bool isNew);
+
+    /// <summary>
+    /// Convenience overload for simple next-bar requests.
+    /// </summary>
+    TBar Next(bool isNew = true);
+
+    /// <summary>
+    /// Retrieves a batch of historical bars.
+    /// </summary>
+    TBarSeries Fetch(int count, long startTime, TimeSpan interval);
+}
+```
+
+## Implementation Guidelines
+
+When implementing `IFeed`:
+
+1. **State Management**: Maintain the current position in the data source.
+2. **End of Data**: When data is exhausted, `Next` should return the last valid bar and set `isNew` to `false`.
+3. **Intra-bar Updates**: If the source supports it (e.g., live ticks), `Next(isNew: false)` should return the updated state of the current bar. If not supported (e.g., CSV), it should return the current bar unchanged.
+4. **Thread Safety**: Implementations are generally not required to be thread-safe unless specified.
+
+## Implementations
+
+* **`GBM`**: Geometric Brownian Motion generator (Synthetic).
+* **`CsvFeed`**: Reads OHLCV data from CSV files (Historical).