Fix mypy errors in example tutorials - #1703

This PR fixes mypy type checking errors in several example tutorial scripts.

Changes made:

• Added checks for Optional values before indexing.
• Ensured safer handling of variables such as tasks and targets.
• Updated example scripts to avoid mypy errors while keeping the tutorial logic unchanged.

Files modified:

• examples/Basics/simple_datasets_tutorial.py
• examples/Basics/simple_suites_tutorial.py
• examples/Basics/simple_flows_and_runs_tutorial.py

All changes were verified by running:

pre-commit run --all-files

and ensuring that mypy checks pass successfully.

Fixes #1696