Simplify `PerRequestServerDataConsumer`

[MarcoRossignoli]

Today in server mode we're trying to batch payloads per-call, we could do better and move the complexity close to the network channel and have a queue there where we can queue "all the in-progress" per call and move this class to a simply proxy.

https://github.com/microsoft/testfx/blob/main/src/Platform/Microsoft.Testing.Platform/ServerMode/PerRequestServerDataConsumerService.cs

AB#1950773

[testplatform-bot]

✅ Successfully linked to Azure Boards work item(s):

• User Story 1950773

[Evangelink]

Pushed back to 3.4

[Evangelink]

Clearing milestone as there is no plan on improving server mode for now.