feat: remove "verbose" verbosity level

[G-Rath]

We're only actually using this level in one place currently, and it is not one of the log levels defined by slog by default - I also think there's an argument to be made that "verbose" itself is something of a mode rather than a level; i.e. it implies maybe all logs should be shown regardless of their level, or debug, or some other combination.

Either way I think we should remove it as part of v2 while we can to make things a bit simpler and we can introduce it back in a minor version if/when we decide to use it.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.57%. Comparing base (caaabe2) to head (d2315bc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1686      +/-   ##
==========================================
- Coverage   64.60%   64.57%   -0.04%     
==========================================
  Files         156      156              
  Lines       16014    15980      -34     
==========================================
- Hits        10346    10319      -27     
+ Misses       4986     4979       -7     
  Partials      682      682              

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