Upgrade Click and ufmt

[HayaoSuzuki]

Summary

• Raise the Click requirement from >=8.0,<8.2 to >=8.3.3,<9 to address PYSEC-2026-2132.
• Update ufmt from 2.8.0 to 2.9.1.
• Click 8.2 removed the mix_stderr parameter from CliRunner and changed Result.output to mix stdout and stderr. Use CliRunner() and assert against Result.stdout in the CLI tests.
• Click 8.2 also changed how groups handle no arguments, which would cause fixit to exit 2 and write help to stderr. Preserve Fixit's existing behavior, in which fixit prints help to stdout and exits 0 while option-only invocations still report a missing command.
• Fixes Out-of-date click dependency has an attached CVE #570
• Unblocks Bump ufmt from 2.8.0 to 2.9.1 #565

Test Plan

• Python 3.10.20 with Click 8.3.3 and ufmt 2.9.1: 391 tests passed.
• Python 3.12.6 with Click 8.5.0 and ufmt 2.9.1: 391 tests passed.
• pyrefly check -c pyproject.toml
• python -m flake8 src/fixit/ scripts/
• python -m fixit lint src/fixit/ scripts/
• python scripts/check_copyright.py
• python -m build
• Sphinx HTML build
• make lint stops at python -m ufmt check, which reports the same 27 paths on this branch and origin/main with Black 26.3.1 from Bump black #560. Flake8, Fixit lint, and the copyright check pass.