More Integration Tests for datadog-trace-agent

[Lewis-E]

What does this PR do?

• Adds full integration tests that covers stat and trace flushing with TCP and Named Pipes

Motivation

• Added partial integration tests in Add Windows Named Pipes to the Trace Agent #58 and figured we might as well go the whole way, but in a separate PR for review-friendliness

Describe how to test/QA your changes

• PR is only tests

[duncanpharvey]

LGTM! Just some minor comments and questions

[kathiehuang]

I got this error when trying to build from main:

error[E0063]: missing field `so_rcvbuf` in initializer of `DogStatsDConfig`
   --> crates/datadog-serverless-compat/src/main.rs:239:28
    |
239 |     let dogstatsd_config = DogStatsDConfig {
    |                            ^^^^^^^^^^^^^^^ missing `so_rcvbuf`

For more information about this error, try `rustc --explain E0063`.

It seems to have just happened to conflict with the previous commit 383fd14 😅