fix: Ensure walk() doesn't error out on directory ENOENT

[nzakas]

What is the purpose of this pull request?

Ensures that walk() doesn't error out on ENOENT errors. Due to the asynchronous nature of listing directory entries, it's possible that a directory may have been deleted before list() is called on it.

Other packages that do this:

• glob - https://github.com/isaacs/node-glob/blob/main/src/processor.ts#L138
• fast-glob - https://github.com/mrmlnc/fast-glob/blob/master/src/providers/filters/error.ts#L18

Refs eslint/eslint#18955

What changes did you make? (Give an overview)

This pull request includes changes to handle directory listing errors more gracefully in the Hfs class and adds corresponding tests to ensure the new behavior is correct. The most important changes include modifying the walk method to handle ENOENT errors, updating the test suite to include a test for this new behavior, and importing necessary error classes.

Error handling improvements:

• packages/core/src/hfs.js: Modified the walk method to catch ENOENT errors and return an empty array instead of throwing an error.

Test suite updates:

• packages/core/tests/hfs.test.js: Added a new test case to verify that the walk method silently skips directories when list() throws an ENOENT error.
• packages/core/tests/hfs.test.js: Imported NotFoundError from errors.js to use in the new test case.