refactor(backend): Reorganize & clean up execution update system (#9663)

- Prep work for #8782
- Prep work for #8779

### Changes 🏗️

- refactor(platform): Differentiate graph/node execution events
- fix(platform): Subscribe to execution updates by `graph_exec_id`
instead of `graph_id`+`graph_version`
- refactor(backend): Move all execution related models and functions
from `.data.graph` to `.data.execution`
- refactor(backend): Reorganize & refactor `.data.execution`

- fix(libs): Remove `load_dotenv` in `.auth.config` to fix test config
issues
- dx: Bump version of `black` in pre-commit config to v24.10.0 to match
poetry.lock

- Other minor refactoring in both frontend and backend

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - Run an agent in the builder
    - [x] -> works normally, node I/O is updated in real time
  - Run an agent in the library
    - [x] -> works normally

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Co-authored-by: Zamil Majdy <[email protected]>