Add target variable highlighting for visualizations

[Copilot]

Target Variable Support Implementation ✅

This PR adds support for specifying a target variable that will be highlighted in visualizations, making it easier to understand relationships between features and the target variable in machine learning tasks.

What's New:

✅ Target Variable Highlighting - Specify a column to highlight throughout all plots

• CLI: --target COLUMN option
• Library: target='column_name' parameter
• Works with both categorical and numeric targets

What Gets Highlighted:

• 📊 Scatter Plots (Numeric vs Numeric): Points colored by target variable
• 📈 Distribution Plots (Single Numeric): Histograms and violin plots grouped by target
• 📊 Bar Plots (Single Categorical): Bars grouped/colored by target

Recent Improvements (addressing code review feedback):

• [x] Fixed missing sharex=True parameter in single variable plots for consistency
• [x] Extracted target validation logic to shared utility function validate_target_variable()
• [x] Removed code duplication between CLI and library interfaces
• [x] CLI now validates target exists in data types
• [x] Library validates target exists in both data types and actual data
• [x] All 148 tests passing

Changes Made:

• [x] Add target parameter to CLI (--target option)
• [x] Add target parameter to library interface
• [x] Add global config for target variable storage
• [x] Update scatter plots to use target for coloring
• [x] Update numeric distribution plots to group by target
• [x] Update categorical plots to use target as hue
• [x] Add comprehensive tests (5 new tests, all passing)
• [x] Update documentation with examples and visual comparison
• [x] Run full test suite (148 tests, all passing)
• [x] Format and lint all code
• [x] Security scan (0 vulnerabilities)
• [x] Address code review feedback

Usage Examples:

CLI:

python -m src data.csv dtypes.json output --target Survived

Library:

import brute_force_plotter as bfp
bfp.plot(data, dtypes, output_path='./plots', target='Survived')

Backward Compatibility:

✅ Fully backward compatible - the target parameter is optional ✅ All existing tests pass without modification ✅ Default behavior unchanged when target is not specified

Test Results:

• Total Tests: 148 (5 new tests added)
• Pass Rate: 100%
• Coverage: ~96%
• All linting checks pass
• Security scan: 0 vulnerabilities

Original prompt

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This section details on the original issue you should resolve

<issue_title>target variable support</issue_title> <issue_description>having support for a target variable.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes eyadsibai/brute-force-plotter#28

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