The key line here is the `-W error` in `tox.ini`. That raises all
warnings (the most common are deprecation and resource) to errors, when
running the unit tests. The bulk of the rest of the PR is cleaning up
tests (and one docstring, because we test those too, via doctest) to
properly clean up resources.

The changes not in the tests (or docs) need more careful examination:
* in `ops.storage` we wrap setup so that if opening the database fails,
we properly clean up. Should never happen in practice (no other process
should be touching the db) and even if it did, we would close on the
crash, but better to tidily manage it, and this also fixes test cases.
* in `ops._main` when instantiating the charm if something goes wrong
(like the charm `__init__` raising) cleanly close the framework.
Definitely could happen in practice, but we would close everyone on the
crash. Doing it explicitly is cleaner in general, and helps when running
tests.
* in `ops.pebble` when handling garage coming back from Pebble, the
`urllib.error.HTTPError` is also a response object and carries the open
HTTP response body in e.fp (we use it already with `.read()` and so on).
Under Python 3.14 there's a tempfile
(python/cpython#15002, which looks unrelated but
look at the code) so we get a warning on exit for failing to clean up.
This could happen in production with a broken Pebble, although again no
real consequence, but nice to clean up for the tests and correctness.

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Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>