feat(backend): Add cost on node & graph execution stats

[majdyz]

Changes 🏗️

Checklist 📋

For code changes:

• I have clearly listed my changes in the PR description
• I have made a test plan
• I have tested my changes according to the test plan:
  • ...

Example test plan

• Create from scratch and execute an agent with at least 3 blocks
• Import an agent from file upload, and confirm it executes correctly
• Upload agent to marketplace
• Import an agent from marketplace and confirm it executes correctly
• Edit an agent from monitor, and confirm it executes correctly

For configuration changes:

• .env.example is updated or already compatible with my changes
• docker-compose.yml is updated or already compatible with my changes
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Examples of configuration changes

• Changing ports
• Adding new services that need to communicate with each other
• Secrets or environment variable changes
• New or infrastructure changes such as databases

[qodo-merge-pro]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 No relevant tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Cost Initialization The cost variable is initialized to 0 but then immediately overwritten by db_client.spend_credits(data). The initial assignment appears unnecessary. cost = 0 try: # Charge the user for the execution before running the block. cost = db_client.spend_credits(data)

[deepsource-io]

Here's the code health analysis summary for commits af8ea93..6626fd9. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
JavaScript	✅ Success		View Check ↗
Python	✅ Success	❗ 19 occurences introduced 🎯 19 occurences resolved	View Check ↗

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