feat(assert): add arrays equal assertion

[SauronBot]

Summary

Adds a first-class assert_arrays_equal assertion for comparing expected and actual arrays separated by --.

Changes

• Parse expected and actual arrays around a -- separator.
• Fail on length mismatch with expected and actual lengths.
• Fail on element mismatch with the differing index.
• Document the new assertion and update the assertion docs snapshot.

Testing

• bash ./bashunit tests/unit/assert_advanced_test.sh --filter arrays_equal
• bash ./bashunit tests/acceptance/bashunit_test.sh --filter display_all_assert_docs
• make test
• bash -n src/assert_arrays.sh

make sa and make lint could not run locally because shellcheck and editorconfig-checker are not installed in this environment.

Closes #639

[Chemaclass]

Nice

[Chemaclass]

Missing chagelog update!