chore(core): always return envelope on sync responses

[jrriehl]

Proposed Changes

Always return the envelope when received as a response to an outgoing sync message. Previously we processed these via the dispatcher if it was there, but this kind of defeats the purpose of sending a message synchronously as it cannot be handled within the same handler from which it was sent.

Also added a default timeout for sync responses.

Linked Issues

[if applicable, add links to issues resolved by this PR]

Types of changes

What type of change does this pull request make (put an x in the boxes that apply)?

• Bug fix (non-breaking change that fixes an issue).
• New feature added (non-breaking change that adds functionality).
• Breaking change (fix or feature that would cause existing functionality to stop working as expected).
• Documentation update.
• Something else (e.g., tests, scripts, example, deployment, infrastructure).

Checklist

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• I have read the CONTRIBUTING guide
• Checks and tests pass locally

If applicable

• I have added tests that prove my fix is effective or that my feature works
• I have added/updated the documentation (executed the script in python/scripts/generate_api_docs.py)