Include contract multiplier in serialized option order value

[sqsge]

What

• fix serialized/exported value for option orders in ReadOrdersResponseJsonConverter
• add a regression test covering option order serialization value
• update option order JSON fixtures to match multiplier-aware serialized output

Why

Issue #8447 reports that exported order value omits the option contract multiplier, so option orders are serialized with quantity * price instead of quantity * price * contract multiplier.

How

• keep the fix local to serialization
• preserve existing behavior for non-option orders
• when serializing option orders, compute value as order.Value * contractMultiplier

Testing

• dotnet build Tests/QuantConnect.Tests.csproj --no-restore -v minimal
• dotnet test Tests/QuantConnect.Tests.csproj --no-build --no-restore --filter FullyQualifiedName=QuantConnect.Tests.Common.Orders.ReadOrdersResponseJsonConverterTests.SerializesOptionOrderValueUsingContractMultiplier -v minimal
• targeted regression test passed locally: 1 passed, 0 failed