Fixes#12280.
# Description
This removes the dependency on the `difference` crate, which is
unmaintained, for `nu-plugin-test-support`. The `similar` crate
(Apache-2.0) is used instead, which is a bit larger and more complex,
but still suitable for a dev dep for tests. Also switched to use
`crossterm` for colors, since `similar` doesn't come with any terminal
pretty printing functionality.
# User-Facing Changes
None - output should be identical.
# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`
