Fix combo update grouped-order retrieval in IBPlaceOrder

[creatidy]

Description

Adjusts IBPlaceOrder grouped-order retrieval behavior:

• For new submissions (needsNewId == true): keep current cache-based grouped retrieval.
• For updates (needsNewId == false): retrieve grouped orders from _orderProvider.GetOrderById(...) so a single-leg update request can reliably reconstruct the full combo group.

Related Issue

#217

Motivation and Context

Combo updates may arrive through one leg/ticket context, where transient cache-based grouped retrieval is insufficient.
This can cause update-path misses and inconsistent combo update behavior.

Using order-provider-based group reconstruction on updates makes update handling reliable and deterministic.

Requires Documentation Change

No.

How Has This Been Tested?

• Build validation:
  • dotnet build /tmp/ib-pr/QuantConnect.InteractiveBrokersBrokerage/QuantConnect.InteractiveBrokersBrokerage.csproj --no-restore
• Also validated with LEAN-side targeted regression tests tied to the companion issue:
  • BrokerageTransactionHandlerTests.ProcessesComboRequestsOnSameThreadWhenConcurrencyIsEnabled
  • BrokerageTransactionHandlerTests.ProcessesOrdersConcurrently

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>

Additional note for tests:
This repository does not currently include a focused unit-test harness for this specific grouped update-path edge case in this change set, so coverage is validated by successful build plus companion LEAN regression tests.