Extend LSMA to accept benchmark reference

[aiSynergy37]

Closes #6984.

Description

Adds a benchmark-reference mode to LeastSquaresMovingAverage so LSMA can regress a target symbol against a reference symbol instead of only regressing target values against a fixed time index.

This adds:

• LeastSquaresMovingAverage(string name, Symbol referenceSymbol, int period) and LeastSquaresMovingAverage(Symbol referenceSymbol, int period) constructors
• QCAlgorithm.LSMA(Symbol symbol, Symbol reference, int period, ...) helper overload
• paired target/reference timestamp handling so the indicator works whether the target or reference update arrives first
• tests for target-first updates, reference-first updates, timestamp matching, and reset behavior

Related Issue

Closes #6984

Motivation and Context

Maintainer guidance requested a Symbol reference overload for LSMA. A previous PR for this issue was closed with concerns around paired-symbol time handling; this implementation waits for matching target/reference timestamps before adding a regression sample.

How Has This Been Tested?

• dotnet build Tests\QuantConnect.Tests.csproj --no-restore --verbosity minimal
• dotnet test Tests\QuantConnect.Tests.csproj --no-build --no-restore --filter "FullyQualifiedName~QuantConnect.Tests.Indicators.LeastSquaresMovingAverageTests" --logger "trx;LogFileName=feature6984-lsma.trx" --logger "console;verbosity=normal" (local test host aborts during test setup with Python.NET GIL finalizer error before executing tests)

Types of Changes

• New feature
• Tests