feat(core): support sync messaging in uagents-core

[jrriehl]

Proposed Changes

Add support for sync messaging in uagents_core

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

Put an x in the boxes that apply:

• 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)

[Copilot]

Pull Request Overview

This PR adds support for synchronous messaging in the uagents-core library, allowing agents to send messages and wait for responses in a blocking manner.

Key changes:

• Added sync parameter to message sending functions to enable synchronous communication
• Implemented response parsing and validation for sync messages with expected response types
• Added appropriate headers for sync message identification

[jrriehl]

Update

• fixed some redundant logic with the with the number of endpoints resolved
• once a message is sent successfully, do not continue to send to other endpoints
• refactored parse envelope response into new function