style: add readonly modifiers to fields in internal classes

Added readonly modifiers to fields that are only assigned in constructors:
- ConvLayer<T>: _kernels, _biases
- TransformerBlock<T>: _weights
- InformerEncoderBlock<T>: _attentionWeights, _ffnWeights
- InformerDecoderBlock<T>: _selfAttentionWeights, _crossAttentionWeights

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ooples

src/TimeSeries/AnomalyDetection/DeepANT.cs

@@ -343,8 +343,8 @@ internal class ConvLayer<T>
     private readonly int _inputChannels;
     private readonly int _outputChannels;
     private readonly int _kernelSize;
-    private Matrix<T> _kernels;
-    private Vector<T> _biases;
+    private readonly Matrix<T> _kernels;
+    private readonly Vector<T> _biases;
 
     public int ParameterCount => _kernels.Rows * _kernels.Columns + _biases.Length;
 

src/TimeSeries/ChronosFoundationModel.cs

@@ -196,7 +196,6 @@ public override T PredictSingle(Vector<T> input)
     public Dictionary<double, Vector<T>> ForecastWithQuantiles(Vector<T> history, double[] quantiles, int numSamples = 100)
     {
         var samples = new List<Vector<T>>();
-        var random = new Random();
 
         for (int s = 0; s < numSamples; s++)
         {
@@ -343,7 +342,7 @@ public ChronosOptions(ChronosOptions<T> other)
 internal class TransformerBlock<T>
 {
     private readonly INumericOperations<T> _numOps;
-    private Matrix<T> _weights;
+    private readonly Matrix<T> _weights;
 
     public int ParameterCount => _weights.Rows * _weights.Columns;
 

src/TimeSeries/InformerModel.cs

@@ -241,8 +241,8 @@ internal class InformerEncoderBlock<T>
 {
     private readonly INumericOperations<T> _numOps;
     private readonly int _embeddingDim;
-    private Matrix<T> _attentionWeights;
-    private Matrix<T> _ffnWeights;
+    private readonly Matrix<T> _attentionWeights;
+    private readonly Matrix<T> _ffnWeights;
 
     public int ParameterCount => _attentionWeights.Rows * _attentionWeights.Columns +
                                   _ffnWeights.Rows * _ffnWeights.Columns;
@@ -292,8 +292,8 @@ internal class InformerDecoderBlock<T>
 {
     private readonly INumericOperations<T> _numOps;
     private readonly int _embeddingDim;
-    private Matrix<T> _selfAttentionWeights;
-    private Matrix<T> _crossAttentionWeights;
+    private readonly Matrix<T> _selfAttentionWeights;
+    private readonly Matrix<T> _crossAttentionWeights;
 
     public int ParameterCount => _selfAttentionWeights.Rows * _selfAttentionWeights.Columns +
                                   _crossAttentionWeights.Rows * _crossAttentionWeights.Columns;