docs: add refactoring plan for consolidating bootstrap logic (#183)

Author: astrogilda

refactoring-plan-183.md

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+# Refactoring Plan for Issue #183: Consolidate Bootstrap Generation Logic
+
+## Overview
+This PR addresses the code duplication in bootstrap generation by consolidating 15+ implementations of `_generate_samples_single_bootstrap`.
+
+## Proposed Solution: Template Method Pattern
+
+### Base Implementation:
+```python
+# In BaseTimeSeriesBootstrap
+def _generate_samples_single_bootstrap(self, X, y=None):
+    """Template method for bootstrap generation"""
+    # Step 1: Validate inputs
+    self._validate_bootstrap_inputs(X, y)
+    
+    # Step 2: Prepare data
+    prepared_data = self._prepare_bootstrap_data(X, y)
+    
+    # Step 3: Generate bootstrap samples (customizable)
+    samples = self._generate_bootstrap_samples(prepared_data)
+    
+    # Step 4: Post-process samples
+    return self._post_process_samples(samples)
+```
+
+## Files affected:
+- All bootstrap implementation files in `src/tsbootstrap/`
+- Base class: `base.py`
+
+## Migration strategy:
+1. Implement template method in base class
+2. Migrate each bootstrap type incrementally
+3. Remove duplicated code
+4. Ensure backward compatibility
+
+## Testing plan:
+- Regression tests for each bootstrap type
+- Verify identical output before/after refactoring
+- Performance benchmarks