Prevent absolute paths from propagating into EEGLAB setname

[laemtl]

Motivation

When exporting EEGLAB .set files, users commonly pass an absolute path as fname.
This path propagates into EEG.setname, resulting in dataset names like:
/full/path/to/sub-01_task-rest.set
This makes EEGLAB datasets non-portable when files are moved or reorganized within a pipeline.

What this PR does

This change ensures that EEG.setname is derived only from the basename stem of fname:
• directory components are removed
• the file extension is stripped

Example:

fname = "/tmp/sub-01_task-rest.set"
EEG.setname == "sub-01_task-rest"

This keeps dataset names portable while leaving all other export behavior unchanged.

Scope of change

•	Introduces a small helper to derive setname from fname
•	Applies this helper at export time in raw.py and epochs.py

Rationale

This aligns with common EEGLAB usage, where setname is a logical dataset identifier rather than a filesystem path, and improves downstream tooling (including MNE-based exports).

[larsoner]

Sounds totally reasonable, thanks @laemtl !

[larsoner]

@laemtl can you fix the style issues?

[laemtl]

@larsoner Done! Not sure how are triggered the linting checks :)

[larsoner]

Thanks @laemtl !

[laemtl]

@larsoner My pleasure! Can I ask when is scheduled the next release? I am using my fork in the meantime, but definitely want to rebase to the official repo as soon as it is available!

[larsoner]

Already cut 2h ago! https://pypi.org/project/eeglabio/0.1.3/

[laemtl]

@larsoner Very impressive. Thank you!!