Add new risk metrics

[akrivi]

This PR implements the following metrics:

• LOLD: as defined in [1]
• LOLEv: as defined in [2]

With the implementation of the above, all metrics defined in [2] are included in PRAS

Additionally, the following metrics commonly used in analysis are implemented:

• MeanEventDuration, MaxEventDurationResult, MeanEventEnergyResult, MaxEventEnergyResult

• Finally, a new events walkthrough has been added to the docs

References:
[1] “Clarifying the interpretation and use of the LOLE Resource Adequacy Metric,”
[2] "Probabilistic Adequacy and Measures", NERC

[Copilot]

Pull request overview

This PR adds new reliability metrics—LOLD (loss of load days), LOLEv (loss of load events), and MeanEventDuration—by introducing a new event-based result type (ShortfallEvents) and extending existing shortfall-sample metrics.

Changes:

• Add new ReliabilityMetric types: LOLD, LOLEv, and MeanEventDuration.
• Implement LOLD computation from ShortfallSamplesResult using day grouping derived from timestamps.
• Introduce ShortfallEvents result recording/finalization to enable event-based metrics and add corresponding simulation tests.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
PRASCore.jl/test/Simulations/runtests.jl	Adds tests for LOLD and event-based metrics (LOLEv/MeanEventDuration).
PRASCore.jl/src/Simulations/utils.jl	Extends init_regionshortfall dispatch to include ShortfallEvents.
PRASCore.jl/src/Simulations/recording.jl	Adds record!/reset! logic to accumulate contiguous shortfall events.
PRASCore.jl/src/Results/utils.jl	Adds _day_ids helper to map timestamps to day identifiers.
PRASCore.jl/src/Results/metrics.jl	Defines new metric structs and show/val/stderror behavior.
PRASCore.jl/src/Results/ShortfallSamples.jl	Implements LOLD constructors and day-counting logic for samples.
PRASCore.jl/src/Results/ShortfallEvents.jl	Adds new ShortfallEvents resultspec, accumulator/result types, and event-based metric constructors.
PRASCore.jl/src/Results/Results.jl	Exports new metrics and includes the new ShortfallEvents result file/type.

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[sriharisundar]

Thanks @akrivi for the PR! Can you please check the test syntax and make sure tests are passing? Also please address any valid copilot comments and resolve them, and whatever you feel are not valid, leave them as it is or reply and I will resolve them.

For the docs, you just need to add the new metrics to the ##Results section in this file - https://github.com/akrivi/PRAS/blob/main/docs/src/PRASCore/api.md and docs should pass.

Please lmk if you want any inputs on getting the tests to pass and we can chat.