fix: snapshot the charts for the in-run results analysis

[Romazes]

Description

The in-run results analysis received the handler's live charts. PortfolioMarginUsageAnalysis enumerates the "Portfolio Margin" chart while the algorithm thread keeps sampling it at midnight, so the enumeration failed:

BacktestingResultHandler.RunInRunResultsAnalysis(): Error running in-run backtest analysis System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.List`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.CastICollectionIterator`1.MoveNext()
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
   at QuantConnect.Lean.Engine.Results.Analysis.Analyses.PortfolioMarginUsageAnalysis.<>c.<Run>b__10_0(KeyValuePair`2 kvp) in Engine/Results/Analysis/Analyses/PortfolioMarginUsageAnalysis.cs:line 66

BacktestingResultHandler.Update() now clones the charts under ChartLock before building the intermediate result, the way the live handler does for its packets, so the in-run analyses and the stored result read a consistent copy. The ResultsAnalyzer.Run doc comment that accepted the torn read is updated.

Side effect: StoreResult no longer strips single-point series from the live margin chart during the run, only from the copy. Stored files and sent packets are unchanged.

Related PR(s)

#9632 added the in-run analysis.

Related Issue

N/A

Motivation and Context

The handler catches the exception and logs it as an error, so the backtest completes, but the error line lands on stderr and the cloud shows it in the backtest error box. Users saw a fatal-looking error on a completed backtest.

Requires Documentation Change

No

How Has This Been Tested?

• New BacktestingResultHandlerTests.InRunAnalysisRunsWhileTheAlgorithmSamplesTheCharts: a 100,000-point margin chart, a task re-sampling its last point under the chart lock, and the handler's update loop running the in-run analysis. Fails on master with the stack above, passes with the fix, 3 reruns.
• BacktestingResultHandlerTests, ResultsAnalyzerInRunTests and ResultsAnalyzerTests: 41 of 41 passed.
• The race is timing based: a cloud backtest with 20 equities, hourly, 1998 to 2024, buy and hold, did not hit it in one run, while the unit test hits it every time.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>