Audit all algorithms to ensure that CancellationError is never explicitly thrown

Came up during a discussion with @FranzBusch - we might need to ensure that CancellationError is never explicitly thrown, as it makes it difficult to combine with typed throws of upstream async sequences.

Start by reviewing all algorithm implementations for explicit CancellationError throws and compare the findings with the typed-throws concern described in the issue. Done means the audit establishes that no algorithm explicitly throws CancellationError; the payload names no specific files or tests.

Written by the indexing model from the issue text.