Add slack bot, progress tracking for protocols and cancellation of protocols

[marcosfrenkel]

Description

This PR adds two main capabilities to the PQN stack:

1. Slack integration for daily CHSH reports — A new script (scripts/chsh_daily_report.py) that runs a CHSH measurement via the API and posts the results to a Slack channel using a configurable webhook URL. The Slack message is dynamically formatted to handle arbitrary result fields.
2. SSE-based progress tracking for protocols — Server-Sent Events (SSE) endpoints added to the chsh, qkd, and rng routes so the frontend can display a live progress/loading bar during long-running protocol measurements.
3. Protocol cancellation propagation — When a user cancels a protocol, the local node now notifies its peer node via a new /coordination/protocol_cancelled endpoint, and an asyncio cancellation event unblocks any waiting operations on both sides.

Motivation and Context

• Users needed visibility into daily CHSH performance without manually querying the API.
• Long-running protocol measurements gave no feedback to the frontend, making it unclear whether the system was working.
• Protocol cancellation was previously local-only; the peer node would hang waiting for a response that would never come.

How have these changes been tested?

• Daily report script tested end-to-end against a running stack instance with a real Slack webhook.
• SSE progress events verified in the browser during live CHSH, QKD, and RNG runs.
• Protocol cancellation tested by cancelling mid-run and confirming the peer node receives and acknowledges the event.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• My code follows the code style of this project.
• My changes require changes to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests pass.