Rollup merge of #141105 - GrantBirki:grantbirki/path-tests, r=jhpratt

additional edge cases tests for `path.rs` 🧪

This pull request adds a few new edge case tests to the `std::path` module. The new tests cover scenarios such as paths with only separators, non-ASCII and Unicode characters, embedded new lines, etc. Each new test is documented with some helpful in-line comments as well.

Author: GuillaumeGomez