WIP: Dynamic transaction thread pool

[JosueNina]

Description

When the brokerage supports concurrency, the transaction handler used a fixed number of threads. This replaces that with a worker pool that starts at minimum-transaction-threads (2) and grows on demand up to maximum-transaction-threads (10) when the workers are busy.

The logic lives in a new generic DynamicWorkerPool<T> class. All requests for the same order are routed to the same queue and processed in order, one at a time, as the pool grows. The synchronous backtest path is unchanged

Motivation and Context

N/A

Requires Documentation Change

N/A

How Has This Been Tested?

It was tested using unit tests.

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> or feature-<issue#>-<description>