Scope the log level set by verbose to the call

[sappelhoff]

Draft for review on the fork before it goes to xdf-modules.

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.

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.

Notes

• Branched from this fork's main, which is one commit behind xdf-modules/main (a
  dependabot actions bump, no code). Rebase before opening upstream.
• The changelog entry cites #175 as the upstream PR number, a guess from #174 being the
  latest. Needs confirming when the upstream PR exists.
• Deliberately left alone: load_xdf sets the level on pyxdf.pyxdf rather than 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.

[sappelhoff]

Submitted upstream as xdf-modules#175.