[fix] Update prompt to handle case with a socket and a host of None (resolves #707)

[scottnemes]

Description

Updates the prompt display logic to handle an edge case where a socket is used without a host being parsed from any other method.

Current behavior when a socket is used and host is None:

MySQL root@none:(none)>

Updated behavior:

MySQL root@localhost:(none)>

Resolves #707

Checklist

• I've added this contribution to the changelog.md.
• I've added my name to the AUTHORS file (or it's already there).
• I ran uv run ruff check && uv run ruff format && uv run mypy --install-types . to lint and format the code.