fix: don't choke on other OS path separators

[mosteo]

Fixes #1984

PR creation checklist

• A test is included, if required by the changes.
• doc/user-changes.md has been updated, if there are user-visible changes.
• doc/catalog-format-spec.md has been updated, if applicable.
• BREAKING.md has been updated for major changes in alr, minor/major in catalog format.

[Copilot]

Pull Request Overview

This PR fixes issue #1984 by handling path separators from different operating systems correctly. The fix prevents the tool from failing when encountering paths with non-native path separators (e.g., backslashes on Unix or forward slashes on Windows).

Key changes:

• Updates path handling logic to scrub non-native separators before processing
• Adds comprehensive test coverage for cross-platform path separator scenarios
• Updates the den dependency to version 0.2 which includes the path scrubbing functionality

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
testsuite/tests/misc/other-slash-in-path/test.yaml	Test configuration for cross-platform path separator handling
testsuite/tests/misc/other-slash-in-path/test.py	Test script that creates directories with non-native separators and verifies proper handling
testsuite/drivers/asserts.py	Minor documentation improvement for assert_substring function
src/alire/alire-directories.adb	Core fix that scrubs paths before processing and improves error handling
deps/den	Updates den subproject commit to include path scrubbing functionality
alire.toml	Updates den dependency version and commit reference