Add `#[DoesNotPerformAssertions]`

[roxblnfk]

Marks a test method (or class) as intentionally not performing assertions, suppressing the automatic Risky status that Testo assigns to Passed tests with an empty assertion history.

Semantics:

• Applicable to methods, functions, and classes (class-level applies to every test in the class).
• A test annotated with the attribute that finishes with Passed and no recorded assertions stays Passed instead of being downgraded to Risky.
• The attribute is a hint about intent only — it does not change failure handling. Exceptions, expectation failures, and recorded assertion failures still mark the test as Failed / Error as usual.
• Useful for smoke tests (e.g. "constructor does not throw"), tests that delegate verification to external tooling (snapshots, mutation testing), or tests that observe side effects via listeners/interceptors outside TestState.