Fix attribute not exist error in io

[MGAMZ]

This pull request makes a small correction to the logic for handling incomplete data batches in kilosort/io.py.

Specifically, it ensures that the correct variable is decremented when the last batch is smaller than expected.

The bug was caught with the following traceback:

Traceback (most recent call last):
  File "/home/zhangyiqin/miniforge3/envs/dbci/lib/python3.13/site-packages/spikeinterface/sorters/basesorter.py", line 270, in run_from_folder
    SorterClass._run_from_folder(sorter_output_folder, sorter_params, verbose)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/zhangyiqin/miniforge3/envs/dbci/lib/python3.13/site-packages/spikeinterface/sorters/external/kilosort4.py", line 341, in _run_from_folder
    ops = compute_preprocessing(ops=ops, device=device, tic0=tic0, file_object=file_object)
  File "/home/zhangyiqin/miniforge3/envs/dbci/lib/python3.13/site-packages/kilosort/run_kilosort.py", line 616, in compute_preprocessing
    bfile = io.BinaryFiltered(ops['filename'], n_chan_bin, fs, NT, nt, twav_min,
                              chan_map, hp_filter, device=device, do_CAR=do_CAR,
    ...<2 lines>...
                              shift=shift, scale=scale, file_object=file_object,
                              batch_downsampling=batch_downsampling)
  File "/home/zhangyiqin/miniforge3/envs/dbci/lib/python3.13/site-packages/kilosort/io.py", line 978, in __init__
    super().__init__(filename, n_chan_bin, fs, NT, nt, nt0min, device,
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     dtype=dtype, tmin=tmin, tmax=tmax, shift=shift,
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     scale=scale, file_object=file_object,
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     batch_downsampling=batch_downsampling)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/zhangyiqin/miniforge3/envs/dbci/lib/python3.13/site-packages/kilosort/io.py", line 654, in __init__
    self.n_batches -= 1
    ^^^^^^^^^^^^^^
AttributeError: 'BinaryFiltered' object has no attribute 'n_batches'. Did you mean: 'n_batches_raw'?

Potential Risk

I am not sure if n_batches has some special usage under other scenarios. But the fix is unlikely to introduce BC as self.n_batches is soon overrided by self.set_downsampling

[Copilot]

Pull request overview

This PR fixes an AttributeError bug in the BinaryRWFile.__init__ method where the code attempted to decrement a non-existent attribute when handling incomplete data batches. The fix ensures that n_batches_raw is decremented instead of the yet-to-be-created n_batches attribute.

• Corrects variable name from self.n_batches to self.n_batches_raw when adjusting for small last batches
• Prevents AttributeError that occurred during preprocessing when the last batch is too small
• Aligns with the proper initialization order where n_batches is created later by set_downsampling()

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (3705cea) to head (284edca).
⚠️ Report is 125 commits behind head on main.

Files with missing lines	Patch %	Lines
kilosort/io.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #1018    +/-   ##
======================================
  Coverage   0.00%   0.00%            
======================================
  Files         33      34     +1     
  Lines       5640    6053   +413     
======================================
- Misses      5640    6053   +413     

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