CAMEL-19545: Replace sleep-based synchronization in camel-stream tests

[rkdfx]

Description

Use flushes and Awaitility-driven waiting in the automated stream tests, and replace the disabled manual test's fixed sleep with a timed latch wait. This removes flaky timing assumptions from the camel-stream test suite.

Target

• I checked that the commit is targeting the correct branch (Camel 4 uses the main branch)

Tracking

• If this is a large change, bug fix, or code improvement, I checked there is a JIRA issue filed for the change (usually before you start working on it).

Apache Camel coding standards and style

• I checked that each commit in the pull request has a meaningful subject line and body.

• I have run mvn clean install -DskipTests locally from root folder and I have committed all auto-generated changes.

AI-assisted contributions

• If this PR includes AI-generated code, commits have proper co-authorship attribution (e.g., Co-authored-by trailers) and the PR description identifies the AI tool used.

[rkdfx]

I'm running the mvn clean install -DskipTests locally but it's failing, it's unrelated to my changes. I'll try to clean and test again - Failed to execute goal io.github.ascopes:protobuf-maven-plugin:4.1.3:generate (default) on project camel-kserve: Generation failed - PROTOC FAILED: Protoc failed with an error. Check the build logs above to find the root cause.