Scope the log level set by verbose to the call

[sappelhoff]

load_xdf(verbose=...) sets the level on the module logger and never restores it:

if verbose is not None:
    logger.setLevel(logging.DEBUG if verbose else logging.WARNING)

So one call reconfigures logging for the rest of the process. Two consequences:

1. It overrides the application. A program that had configured pyxdf to its liking
   loses that configuration to any library that happens to call load_xdf(verbose=False) —
   silently, and from code the application does not own.
2. It breaks the documented meaning of verbose=None. The docstring says None "will
   use root logger level", which holds only while the logger's own level is NOTSET. After
   any earlier call that passed verbose, the logger has a level of its own and no longer
   inherits, so every later verbose=None call silently keeps the old setting.

The fix restores the level when the call returns, via a small decorator so the body of
load_xdf is untouched and its signature is preserved through functools.wraps:

@_scoped_log_level
def load_xdf(...):

verbose keeps working exactly as documented during the call; it just no longer leaks out
of it. Restoration happens on the error path too, which is where a leak is most likely to go
unnoticed.

load_xdf is the only function that needs this: it is the only place in the package that
calls setLevel. resolve_streams and match_streaminfos take no verbose and never
change the level, so they log at whatever level is in effect, which is the correct behaviour
for a library.

Tests

test/test_logging.py, 7 cases, no data files needed — they use a nonexistent path so
load_xdf raises after the level has been set:

• the level is unchanged after the call for verbose in (None, True, False)
• a level the application set beforehand survives a verbose=True call
• verbose still decides whether the "Importing XDF file" record is emitted, so the fix
  cannot be mistaken for deleting the feature

Against the current release these fail as expected — assert 10 == 40, the logger left at
DEBUG where the application had set ERROR.

pytest test/: 366 passed, 13 skipped, 1 xfailed. ruff check and ruff format --check
clean.

Note

Deliberately left alone: load_xdf sets the level on pyxdf.pyxdf rather than on the
pyxdf parent, so while a call is in flight it still overrides a level set on the parent
namespace. Now that the override is scoped to the call, that is a much smaller wart, and
changing which logger is addressed would be a behaviour change rather than a fix. Happy to
follow up separately if you would rather it addressed the package logger.

[cbrnr]

Why a decorator though?

[sappelhoff]

Why a decorator though?

What did you have in mind?

Wrapping it into a context manager or a try/finally would lead to a lot of indentations.

And resetting "manually" before each return seems a bit more unclean 🤔

[cbrnr]

Yes, a decorator is cleanest here. I've tweaked it a little bit though:

1. It now contains the setting part as well.
2. I've renamed it to verbose (like in MNE-Python)
3. verbose=None is a no-op.

However, all of this wouldn't be necessary if we removed verbose from the function parameter list. I don't think this function should change global logging state in the first place; instead, a user can set the desired log level outside the function call. So ideally I'd want to remove the parameter, but we can merge this PR as a quick improvement.

[cbrnr]

Thanks @sappelhoff!