fix(core): skip NotFound during concurrent recursive listing

[Xuanwo]

Which issue does this PR close?

Closes #.

Rationale for this change

Behavior tests for fs can fail intermittently under concurrent execution with errors like:

NotFound (persistent) at list ... source: No such file or directory (os error 2)

The failure happens when recursive list traverses entries that are removed by other concurrent tests. In this case, treating NotFound as a hard failure makes list behavior flaky.

What changes are included in this PR?

• Update FlatLister to tolerate ErrorKind::NotFound during recursive traversal by skipping disappeared entries/directories and continuing listing.
• Update FsLister to handle transient NotFound from next_entry, file_type, and metadata paths:
  • end listing gracefully if the listed directory disappears;
  • skip entries that disappear between readdir and metadata probing.
• Keep non-NotFound errors unchanged.

Are there any user-facing changes?

No API changes. Runtime behavior becomes more resilient for concurrent list/delete races.

AI Usage Statement

This PR was developed with Codex (GPT-5) assistance, with human review.

[tisonkun]

Still failed. But unblock the process once you get all the CI checks pass.

[Xuanwo]

• Behavior Test / binding_c / ubuntu-latest / redb / redb (pull_request)

fs is passing, other failure might be related to GHA, will retry them