Collect CLI arguments into a dataclass

[rolandwalker]

Description

Using library clickdc, collect CLI arguments into a cli_args dataclass.

A small amount of reordering was done, which affects the output of the helpdoc, but the intention is for this to introduce no other functional changes.

The properties in cli_args are sometimes mutated, for example when reading comparable values from a DSN. But mutating the properties is debatable.

New tests are introduced for the crucial user/host/port/socket coordinates, but we stop short of adding new tests for every single CLI argument.

Motivations

• clarity
• click_entrypoint() had too many positional arguments
• adding an CLI argument required adding both a decorator and a matching positional argument to click_entrypoint()
• this work can be a step toward breaking up massive main.py and test_main.py

Another related step would be gathering disparate runtime settings into a self.settings property.

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]

No correctness or security regressions stood out in the PR’s code changes.

1. Low: missing precedence regression tests for clickdc migration

• After moving CLI parsing into CliArgs, envvar-backed options now depend on clickdc behavior for precedence (--option vs envvar).
• Current added tests validate “CLI only” and “envvar only”, but not “both set at once”.
• Add explicit cases to ensure CLI values override envvars for user/host/port/socket.
• Relevant code: main.py, main.py
• Existing tests to extend: test_main.py, test_main.py, test_main.py, test_main.py

I couldn’t execute the test suite locally in this environment because pytest is not installed.