feat(rlp): add helpful assert message upon client initialization error in simulator

[danceratopz]

🗒️ Description

This PR adds a more helpful message in the case that the simulator fails to connect to the client container. Currently, in the UI, we have the somewhat unhelpful:

🔗 Related Issues

This was initially hidden by the bug fixed in #569.

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md SKIP.
• All: Considered updating the online docs in the ./docs/ directory.
• Tests: All converted JSON/YML tests from ethereum/tests have been added to converted-ethereum-tests.txt.
• Tests: Included the type and version of evm t8n tool used to locally execute test cases: e.g., ref with commit hash or geth 1.13.1-stable-3f40e65.
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.

[spencer-tb]

Tried and tested! LGTM :)