Add DateRules.QuarterStart and DateRules.QuarterEnd

[AlexCatarino]

Summary

• Adds DateRules.QuarterStart and DateRules.QuarterEnd (no-symbol, string symbol, and Symbol overloads), mirroring the existing MonthStart/MonthEnd and YearStart/YearEnd API.
• Introduces QuarterIterator helper using BaseIterator so behaviour (offsets, boundaries, extended market hours, holidays) matches the existing month/year rules.
• Tests covering no-symbol, no-symbol with offset, no-symbol mid-quarter start, with symbol, end-of-quarter (with and without offset), and offset-out-of-range validation for both methods.

Closes #9453

Test plan

• dotnet test Tests/QuantConnect.Tests.csproj --filter FullyQualifiedName~DateRulesTests (45 passed)