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/numerics/change/Change.md

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+# CHANGE: Relative Price Change
+
+> "The simplest measure of movement is often the most powerful."
+
+CHANGE calculates the percentage change between the current value and a value N periods ago. This fundamental indicator forms the basis for momentum analysis, rate of change calculations, and relative performance comparisons.
+
+## Mathematical Foundation
+
+The change calculation is straightforward:
+
+$$
+\text{Change}_t = \frac{P_t - P_{t-n}}{P_{t-n}}
+$$
+
+where:
+- $P_t$ = current price
+- $P_{t-n}$ = price N periods ago
+- Result is expressed as a decimal (multiply by 100 for percentage)
+
+### Edge Cases
+
+- **Division by zero**: When $P_{t-n} = 0$, returns 0
+- **NaN/Infinity inputs**: Uses last valid value substitution
+
+## Performance Profile
+
+### Operation Count (Per Bar)
+
+| Operation | Count | Notes |
+| :--- | :---: | :--- |
+| Subtraction | 1 | Current - Past |
+| Division | 1 | Conditional on past ≠ 0 |
+| Buffer access | 1 | Ring buffer lookup |
+| **Total** | **~3** | O(1) constant time |
+
+### Quality Metrics
+
+| Metric | Score | Notes |
+| :--- | :---: | :--- |
+| **Accuracy** | 10/10 | Exact mathematical calculation |
+| **Timeliness** | 10/10 | No lag beyond lookback period |
+| **Smoothness** | 3/10 | Raw returns are noisy |
+| **Memory** | 9/10 | Only stores period+1 values |
+
+## Validation
+
+| Library | Status | Notes |
+| :--- | :---: | :--- |
+| **TA-Lib** | ✅ | ROC function (divide by 100) |
+| **Skender** | ✅ | Roc indicator |
+| **Manual** | ✅ | Direct calculation verified |
+
+## Common Pitfalls
+
+1. **Percentage vs Decimal**: QuanTAlib returns decimal (0.1 = 10%), while TA-Lib ROC returns percentage (10.0 = 10%). Multiply by 100 when comparing.
+
+2. **Warmup Period**: Requires `period + 1` bars before producing meaningful results. First `period` values return 0.
+
+3. **Zero Division**: When the past value is zero, returns 0 rather than NaN/Infinity.
+
+4. **Compounding**: For multi-period returns, geometric compounding may be more appropriate than simple arithmetic change.
+
+## Usage Examples
+
+```csharp
+// Period-1 change (simple return)
+var change = new Change(1);
+
+// 10-period momentum
+var momentum = new Change(10);
+
+// Chained from another indicator
+var smaChange = new Change(new Sma(20), 5);
+```
+
+## References
+
+- Murphy, J. (1999). "Technical Analysis of the Financial Markets." New York Institute of Finance.
+- Pring, M. (2002). "Technical Analysis Explained." McGraw-Hill.