Update cli_helpers to v2.12.0

[rolandwalker]

Description

Update cli_helpers to v2.12.0, fixing a preserve_whitespace keyword argument bug with the tabulate library.

Fixes #1699, which should not happen, but does happen.

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 .

[github-actions]

1. Missing regression test for the reported bug fix
   The PR updates cli_helpers to pick up a preserve_whitespace/tabulate fix, but there is no accompanying test in this repo to lock in expected behavior. If cli_helpers behavior changes again, this can silently regress.
   Relevant refs: pyproject.toml:19, main.py:1828, test_tabular_output.py
   Action: add a regression test that formats rows with leading/trailing/internal spaces and asserts whitespace is preserved in tabular output.

2. Version mismatch in changelog entry (likely typo)
   Dependency is pinned to cli_helpers ~= 2.12.0, but changelog says v0.12.0. This can confuse release/debug workflows.
   Relevant refs: pyproject.toml:19, changelog.md:14
   Action: update changelog to v2.12.0 (if that is the intended version).

No direct security issues found in the introduced diff.