Allow more shell-style redirects with /source

[rolandwalker]

Description

Previously

/source "filename.sql" $> output.csv;

would only work if "filename.sql" was quoted, due to a quirk in how we approach detection of valid SQL on the left-hand-side using sqlglot.

With this change, we allow any /source expression on the LHS of a shell-style redirect operator.

The key change is a quite small addition to hybrid_redirection.py, but requires reorganizing several methods to avoid a circular import.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .