Add comprehensive provider coverage tests to ensure runtime and playground consistency.

[kheiner]

Currently the test suite does not validate against alignment between runtime providers and playground configuration. Tests are missing or invalid as a result.

Missing Tests

• Bunny (test is written as a .todo() in test: improve coverage and strictness #2193 )
• Caisy (test is written as a .todo() in test: improve coverage and strictness #2193 )
• Directus
• Filerobot (test is written as a .todo() in test: improve coverage and strictness #2193 )
• GitHub

It would be a lot easier if the tests were organized alphabetically and a provider-coverage test for:

• Each provider should exist exactly once in playground
• Each provider should be defined with a key and value in every image
• All playground providers should exist in runtime
• Images should not contain unknown providers
• Missing provider tests list should shrink over time