Propagate per-entry errors from Path.list!

[lukewilliamboswell]

Context

hosted_dir_list currently discards errors produced while iterating an otherwise successfully opened directory:

let entries = read_dir
    .filter_map(|entry| entry.ok().map(|entry| entry.path()))
    .collect();

See src/lib.rs:1173-1177.

This can return an incomplete list as Ok when an entry disappears during iteration or the filesystem reports an I/O error. Because Path.list! already returns a Try, silently returning partial data is surprising and can lead applications to make incorrect decisions.

Suggested direction

Collect the iterator as a Result<Vec<_>, io::Error> and map the first entry error through the existing directory error conversion. If partial results are considered useful, expose them through a deliberately different API and result type.

Acceptance criteria

• An error from any ReadDir entry is not silently dropped.
• Path.list! returns either a complete snapshot-like result or a typed error.
• Tests exercise the error branch through a controllable abstraction or filesystem race harness.
• Existing success and non-directory cases continue to pass on Unix and Windows.