Disallow panics, unreachables, and expects using clippy lints

[poljar]

Now that we're relatively stable, we can disallow the usage of these quite dangerous invocations.

We don't want to let any of those slip through reviews and it allows people that write PRs know ahead of time that they shouldn't be used.

Depends on #204 since that removes a panic that shouldn't exist.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.38%. Comparing base (3d655ad) to head (ca06697).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #205   +/-   ##
=======================================
  Coverage   90.38%   90.38%           
=======================================
  Files          34       34           
  Lines        1986     1986           
=======================================
  Hits         1795     1795           
  Misses        191      191           

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