⚡️ Improve backend test performance by patching password hashing

[saltie2193]

Improve performance of backend tests by patching password hashing during tests.

NOTE: To reduce interference with preexisting data, all existing users and items are now deleted before the tests are run.
This should not be noticable outside of testing, since all users and items already have been deleted after testing anyway.

[mdrxy]

This substantially reduces testing time - thank you!

Only thing I noticed is that session.execute should become session.exec due to deprecation.

[saltie2193]

At least according to mypy, session.exec of a SQLModel Session does not have an overload that would allow for passing a delete statement. Using it will fail the linting.
However it seems to work anyway.

mypy output when using session.exec:

app/tests/conftest.py:28: error: No overload variant of "exec" of "Session" matches argument type "Delete"  [call-overload]
app/tests/conftest.py:28: note: Possible overload variants:
app/tests/conftest.py:28: note:     def [_TSelectParam] exec(self, statement: Select[_TSelectParam], *, params: Mapping[str, Any] | Sequence[Mapping[str, Any]] | None = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: dict[str, Any] | None = ..., _parent_execute_state: Any | None = ..., _add_event: Any | None = ...) -> TupleResult[_TSelectParam]
app/tests/conftest.py:28: note:     def [_TSelectParam] exec(self, statement: SelectOfScalar[_TSelectParam], *, params: Mapping[str, Any] | Sequence[Mapping[str, Any]] | None = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: dict[str, Any] | None = ..., _parent_execute_state: Any | None = ..., _add_event: Any | None = ...) -> ScalarResult[_TSelectParam]
app/tests/conftest.py:29: error: No overload variant of "exec" of "Session" matches argument type "Delete"  [call-overload]
app/tests/conftest.py:29: note: Possible overload variants:
app/tests/conftest.py:29: note:     def [_TSelectParam] exec(self, statement: Select[_TSelectParam], *, params: Mapping[str, Any] | Sequence[Mapping[str, Any]] | None = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: dict[str, Any] | None = ..., _parent_execute_state: Any | None = ..., _add_event: Any | None = ...) -> TupleResult[_TSelectParam]
app/tests/conftest.py:29: note:     def [_TSelectParam] exec(self, statement: SelectOfScalar[_TSelectParam], *, params: Mapping[str, Any] | Sequence[Mapping[str, Any]] | None = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: dict[str, Any] | None = ..., _parent_execute_state: Any | None = ..., _add_event: Any | None = ...) -> ScalarResult[_TSelectParam]
Found 2 errors in 1 file (checked 38 source files)

I'm not sure what's the better option here. Do we ignore the type checker and provided signature for session.exec? Or, do we insist on not using deprecated methods were it seems like there is no replacement?