DWMA Indicator implementation and tests

lib/trends/dwma/Dwma.md

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+# DWMA - Double Weighted Moving Average
+
+DWMA is a moving average that applies the Weighted Moving Average (WMA) twice. It provides a smoother curve than a standard WMA but with slightly more lag.
+
+## Core Concepts
+
+* **Double Smoothing:** Applies WMA smoothing twice to reduce noise further.
+* **Weighted:** Gives more weight to recent data points, similar to WMA.
+* **Recursive Calculation:** Uses the efficient O(1) WMA implementation.
+
+## Parameters
+
+| Parameter | Type | Default | Description |
+| :--- | :--- | :--- | :--- |
+| `period` | `int` | - | The lookback period for both WMA passes. |
+
+## Formula
+
+$$
+DWMA_t = WMA(WMA(Price, n), n)
+$$
+
+Where:
+
+* $WMA$ is the Weighted Moving Average.
+* $n$ is the period.
+
+## C# Implementation
+
+### Standard Usage
+
+```csharp
+// Create DWMA with period 14
+var dwma = new Dwma(14);
+
+// Update with new value
+var result = dwma.Update(new TValue(DateTime.Now, 123.45));
+Console.WriteLine($"DWMA: {result.Value}");
+```
+
+### Span API (High Performance)
+
+```csharp
+// Calculate on a span of data
+ReadOnlySpan<double> input = ...;
+Span<double> output = new double[input.Length];
+
+Dwma.Calculate(input, output, 14);
+```
+
+### Bar Correction
+
+```csharp
+// Update with a value
+dwma.Update(new TValue(time, 100), isNew: true);
+
+// Correct the last value
+dwma.Update(new TValue(time, 101), isNew: false);
+```
+
+## Interpretation
+
+DWMA is used similarly to other moving averages to identify trends. Due to the double smoothing, it is less susceptible to whipsaws than WMA but reacts slower to price changes.
+
+## References
+
+* [Pine Script Implementation](https://github.com/mihakralj/pinescript/blob/main/indicators/trends_FIR/dwma.md)