Refactor Metric class to separate definition from value and optimize memory usage

[AumPatel1]

The Metric class currently mixes two concerns:

• Metric definition (what the metric is: name, comparison method)
• Metric value(a specific measurement: the numeric value)

This causes:

• Memory inefficiency: Each solution creates a new MetricComparator instance even when using the same comparison method
• Conceptual confusion: The class violates single responsibility principle
• TODO comment in code indicates this needs refactoring (line 101 in metric.py)

Expected Behavior

• Separate metric type definition from metric value
• Share comparator instances across all solutions using the same comparison method
• Reduce memory usage by reusing comparator objects
• Maintain full backward compatibility with existing API

Impact
When running with max_iterations=10, we create 10 identical MetricComparator objects instead of sharing one. This wastes memory and makes the code harder to maintain.

[AumPatel1]

Thats resolved on pr #154