Log through pyprep's own logger namespace

[sappelhoff]

pyprep used three logging mechanisms at once: find_noisy_channels and ransac logged
through MNE's logger (from mne.utils import logger), reference through a handler-less
pyprep.reference logger, and removeTrend straight to the root logger. So pyprep's
records were attributed to mne, could only be silenced through mne.set_log_level, and two
of them surfaced as WARNING:root:....

pyprep now owns a pyprep logger, configured when the package is imported: INFO, its own
handler on sys.stdout, propagate = False. That is the model MNE uses for its own logger,
and the root logger stays untouched. setup_logging is the knob:

pyprep.setup_logging("WARNING")       # warnings and errors only
pyprep.setup_logging(propagate=True)  # let the application's handlers print them

Behaviour change

mne.set_log_level() no longer affects pyprep. Downstream code that relied on it — including
the two examples and the test fixtures in this repo — needs pyprep.setup_logging() instead.
The changelog says so.

Notes

• The four logger.info calls in reference become visible for the first time.
• removeTrend's message said "detreding"; fixed while touching the line.
• tests/conftest.py gains an autouse fixture that quiets pyprep for the suite and restores
  propagation, without which caplog cannot see pyprep records at all: they no longer reach
  the root-level handler pytest installs.

Verification

pytest: 53 passed. In a fresh interpreter with no logging configuration, import pyprep is
now enough to get formatted [INFO] pyprep.<module>: ... on stdout, while
logging.getLogger().handlers is still [].

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.92%. Comparing base (f0e2fae) to head (8773bc4).

Files with missing lines	Patch %	Lines
pyprep/removeTrend.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
+ Coverage   97.85%   97.92%   +0.06%     
==========================================
  Files           7        8       +1     
  Lines         841      869      +28     
==========================================
+ Hits          823      851      +28     
  Misses         18       18              

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