feat: Implement dose calculation fix and enhance legend feature

- Fixed dose calculation logic in `_calculate_daily_dose` to correctly parse timestamps with multiple colons.
- Added comprehensive test cases for various dose formats and edge cases in `test_dose_calculation.py`.
- Enhanced graph legend to display individual medicines with average dosages and track medicines without dose data.
- Updated legend styling and positioning for better readability and organization.
- Created new tests for enhanced legend functionality, including handling of medicines with and without data.
- Improved mocking for matplotlib components in tests to prevent TypeErrors.

tests/conftest.py

@@ -89,3 +89,33 @@ def sample_dose_data():
         'nan_value': 'nan',  # Should be 0
         'no_units': '2025-07-28 18:59:45:10|2025-07-28 19:34:19:5',  # Should sum to 15
     }
+
+
+@pytest.fixture
+def legend_test_dataframe():
+    """DataFrame specifically designed for testing legend functionality."""
+    return pd.DataFrame({
+        'date': ['2024-01-01', '2024-01-02', '2024-01-03'],
+        'depression': [3, 2, 4],
+        'anxiety': [2, 3, 1],
+        'sleep': [4, 3, 5],
+        'appetite': [3, 4, 2],
+        # Medicine with consistent doses for average testing
+        'bupropion': [1, 1, 1],
+        'bupropion_doses': ['2024-01-01 08:00:00:100mg',
+                           '2024-01-02 08:00:00:200mg',
+                           '2024-01-03 08:00:00:150mg'],  # Average: 150mg
+        # Medicine with varying doses
+        'propranolol': [1, 1, 0],
+        'propranolol_doses': ['2024-01-01 12:00:00:10mg',
+                             '2024-01-02 12:00:00:20mg',
+                             ''],  # Average: 15mg (10+20)/2
+        # Medicines without dose data
+        'hydroxyzine': [0, 0, 0],
+        'hydroxyzine_doses': ['', '', ''],
+        'gabapentin': [0, 0, 0],
+        'gabapentin_doses': ['', '', ''],
+        'quetiapine': [0, 0, 0],
+        'quetiapine_doses': ['', '', ''],
+        'note': ['Test note 1', 'Test note 2', 'Test note 3']
+    })