fix: do not wrap --health-cmd in quotes

[aksiksi]

We cannot wrap the health command with single quotes because Nix calls escapeShellArg under the hood on each entry in the ExtraOptions array.

This results in us passing in the single-quote wrapped command as-is - i.e., including single quotes - to the runtime, which causes the entire quote-enclosed string to be interpreted as an executable rather than a shell command.

I have also added a simple health check to the integration test.

Fixes #22.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.31%. Comparing base (3cc5f14) to head (08eefbc).
Report is 1 commits behind head on main.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #25   +/-   ##
=======================================
  Coverage   73.31%   73.31%           
=======================================
  Files           6        6           
  Lines         873      873           
=======================================
  Hits          640      640           
  Misses        197      197           
  Partials       36       36           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.