fix(config): report cache cleanup deletion failures

[solanaXpeter]

Motivation

Cache cleanup paths currently ignore all deletion errors.
That keeps missing paths best-effort, but it also hides permission and path-type failures while leaving stale cache state behind.

Solution

Ignore only io::ErrorKind::NotFound for cache cleanup removals and return all other deletion errors with path context from cleanup and the clean_foundry_* helpers.
Add focused unit tests for missing-path and wrong-path-type cases.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[mablr]

lgtm, thanks!

[decofe]

Cache cleanup is best-effort by design — this PR makes forge clean strictly worse by short-circuiting on the first deletion error (remaining dirs never get cleaned).

Instead of propagating errors, log them and continue. Since sh_warn! is a circular dependency in the config crate, use the same eprintln! + yansi::Paint::yellow pattern already used elsewhere in this file (see L1213):

// Instead of helper functions + Result propagation, just warn and continue:
if let Err(err) = fs::remove_file(&self.test_failures_file) {
    if err.kind() != io::ErrorKind::NotFound {
        eprintln!(
            "{}",
            yansi::Paint::yellow(&format!(
                "Warning: failed to remove test failures file {}: {err}",
                self.test_failures_file.display()
            ))
        );
    }
}

Same pattern for every remove_dir_all call. This way all cleanup steps always run, failures are visible to the user, and forge clean never aborts halfway through.

The helper functions (remove_file_if_exists, remove_dir_all_if_exists) and their tests can be dropped — they're not needed with this approach.

[zerosnacks]

Hi @solanaXpeter, thanks for your PR!

I've decided to implement an alternative approach here: #14379 that I prefer and added you as a co-author