Fix #8447: serialize order value with contract multiplier

[aiSynergy37]

What

• Fixes order JSON serialization so �alue includes the symbol contract multiplier.
• Adds regression coverage for option order serialization value in ReadOrdersResponseJsonConverterTests.
• Updates option order fixture JSON values (camel and capital case) to the multiplier-adjusted value.

Why

Issue #8447 reports that serialized order value used Order.Value (quantity * price), which omits contract multiplier and is incorrect for derivatives like options.

How

• In ReadOrdersResponseJsonConverter.WriteJson, compute serialized value using symbol properties from SymbolPropertiesDatabase and override jObject[value] with order.Value * contractMultiplier.
• Keep existing behavior unchanged when order/symbol is unavailable.
• Add a focused unit test asserting option serialization emits the multiplier-adjusted value.

Testing

• Attempted: dotnet test Tests/QuantConnect.Tests.csproj --filter FullyQualifiedName~ReadOrdersResponseJsonConverterTests
• Note: test execution is currently blocked in this environment by repository package vulnerability warnings (NU1902/NU1903/NU1904) that are treated as build-failing during package asset resolution.