This pull request introduces significant enhancements to the metrics loading and processing pipeline, primarily by adding support for threshold expressions and improving metric definition handling. The changes affect how metrics are parsed, transformed, and evaluated, with new fields and logic for threshold expressions, more robust filtering, and improved naming consistency.

Metric Definition and Threshold Support

• Extended the MetricDefinition struct to include fields for LegacyName, Category, Level, ThresholdExpression, ThresholdVariables, and ThresholdEvaluable, enabling richer metric metadata and threshold evaluation. [1] [2]
• Added logic to extract, transform, and initialize threshold expressions and their variables, ensuring threshold expressions are parsed and evaluable like main metric expressions. [1] [2] [3] [4]

Perfmon Loader Improvements

• Refactored metric filtering to use MetricName instead of LegacyName for more consistent identification, and improved error handling when metrics are missing. Added helper functions for finding metrics by both names. [1] [2] [3]
• Added support for loading and transforming threshold expressions from perfmon metric definitions, including alias replacement and format conversion.

Code Consistency and Usability

• Updated metric printing and summary functions to accept and use the enhanced metric definitions, ensuring all output and summaries reflect the new fields and threshold support. [1] [2] [3] [4]
• Standardized metric naming in output, using LegacyName without the metric_ prefix for improved readability.

Miscellaneous

• Improved transformation logic for metric and threshold expressions, handling conditional formats and logical operators more robustly.
• Added utility imports and code organization for new functionality.

These changes collectively make the metrics system more extensible and robust, especially in handling thresholds and ensuring consistent metric identification across loaders and output.