Race Condition in ScenarioEndpoint Due to LIFO Stack

[tschlat]

As pointed out by @bbortt in #328:
When two identical simulations are triggered nearly simultaneously (within milliseconds), the current ScenarioEndpoint implementation, which uses a LIFO stack, may associate the result of one simulation with the wrong request.

⚠️ Problem
Simulation 1 arrives

Simulation 2 arrives shortly after

Simulation 1 finishes and pushes its result

The stack pops the result, but it may be consumed by Simulation 2, violating the expected request-response association.

This leads to cross-contamination between simulations that should remain isolated.

✅ Solution
The stack has been replaced with a FIFO queue to ensure more predictable behavior. While this doesn't eliminate the theoretical risk of race conditions, the likelihood of misassignment is significantly reduced:

With a queue:

Simulation 1 finishes → result goes to Simulation 1

Simulation 2 finishes → result goes to Simulation 2

Only if Simulation 2 finishes before Simulation 1, and the queue is misused, could a mismatch still occur — but this is far less likely, especially with identical simulations where timing remains synchronized.

🔧 Additional Changes
Upgraded Citrus Core dependency to v4.6.0.

[bbortt]

forget the "additional changes" - I've already merged these in a different PR!