Function clean_benchmark 

pub fn clean_benchmark(name: &str) -> Result<(), BenchError>

Removes the cache directory for a specific benchmark.

A non-existent cache directory is treated as success (idempotent).

Errors

Returns a BenchError if:

• BenchError::NoCacheDir — the platform cache directory is not available.
• BenchError::Io — the directory exists but cannot be removed.