Fix up phpstan issues and formatting in templates and setup CI to run on generated example templates.

[SpencerMalone]

Overview

This is a style cleanup and analysis sweep of the templates to try and get them matching the code quality elsewhere.

What this PR does / why we need it

1. I ran php-cs-fixer a bunch on the generated templates, but sadly couldn't get that into CI because it desperately wanted to fix the class names to be short instead of the FQDN. I figure we can do this later
2. I ran phpstan on the templates and fixed a bunch of minor things with that
3. I tried to setup CI to run phpstan on the templates, I'm not fullyyyyy sure I set all that up right, I'm relatively unfamiliar with dagger but hopefully I figured it out?

Special notes for your reviewer

Does this PR introduce a user-facing change?

Cleanup up code style and typing throughout generated code.

[SpencerMalone]

Here's an execution where I made a failing change to a template: https://github.com/twirphp/twirp/actions/runs/20838658367/job/59868408300?pr=236

Here's an execution with lib/ failing: https://github.com/twirphp/twirp/actions/runs/20838717364/job/59868568606?pr=236

[SpencerMalone]

Also lemme know if this is too large, I just sort of went down the list of reported issues on this one

[sagikazarmark]

Thanks!

I had a couple comments.

[sagikazarmark]

Thanks @SpencerMalone !