feat(matplotlib): implement heatmap-correlation

[claude]

Summary

Implements heatmap-correlation for matplotlib library.

Parent Issue: #53
Sub-Issue: #54
Attempt: 1/3

Implementation

• plots/matplotlib/imshow/heatmap-correlation/default.py

Features

• Creates correlation matrix heatmap using matplotlib's imshow()
• Displays correlation coefficients with diverging color scheme (RdBu_r)
• Shows correlation values in cells formatted to 2 decimal places
• Variable names as axis labels with 45° rotation for readability
• Color bar legend showing scale from -1 to 1
• Clear cell boundaries with subtle grid
• Automatic text color adjustment based on background (white on dark, black on light)
• Centered color scale at 0

Testing

Successfully tested with sample weather data showing correlations between:

• Temperature
• Humidity
• Pressure
• Wind Speed
• Rainfall

The implementation follows all matplotlib library rules and quality criteria.

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