`ex.export_coverage` fails with `PanicException: No data was written.`

Hey Kai,

Running into an error when using the export_coverage function with mostly defaults:

import snapatac2 as snap
print(snap.__version__)  # 2.5.2

adata = snap.read(
    "clustered.h5ad", 
    backed="r+"
)

snap.ex.export_coverage(
    adata=adata,
    groupby="integrated_manual_cellid_annotation",
    suffix=".bw",
    output_format="bigwig",
    out_dir="./bigWigs",
)

2024-01-16 08:48:55 - INFO - Exporting fragments...
2024-01-16 08:49:52 - INFO - Creating coverage files...
thread '<unnamed>' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bigtools-0.2.5/src/utils/file/tempfilebuffer.rs:193:21:
No data was written.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread '<unnamed>' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bigtools-0.2.5/src/utils/file/tempfilebuffer.rs:193:21:
No data was written.
thread '<unnamed>' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bigtools-0.2.5/src/utils/file/tempfilebuffer.rs:193:21:
No data was written.
thread '<unnamed>' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bigtools-0.2.5/src/utils/file/tempfilebuffer.rs:193:21:
No data was written.
thread '<unnamed>' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bigtools-0.2.5/src/utils/file/tempfilebuffer.rs:193:21:
No data was written.
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/cellar/users/aklie/opt/miniconda3/envs/scverse-lite-py39/lib/python3.9/site-packages/snapatac2/export/__init__.py", line 202, in export_coverage
    return internal.export_coverage(
pyo3_runtime.PanicException: No data was written.

It looks like fragments are exported properly (I'm also able to run ex.export_fragments with no problems), but data isn't able to be written to bigWig. I tried writing bedgraph as well and in that case the command completes, but the output files are empty.

I put the h5ad object on Google Drive if you want to take a look (https://drive.google.com/file/d/1gR3mattDYgo9m4YPV2TqpCl7hYRNtAeO/view?usp=drive_link)

I also was able to reproduce this error with the tutorial dataset (pbmc5k):

import snapatac2 as snap
print(snap.__version__)

file_path = snap.datasets.pbmc5k("annotated_h5ad")
adata = snap.read(file_path)

snap.ex.export_coverage(
    adata=adata,
    groupby="cell_type",
    suffix=".bw",
    output_format="bigwig",
    out_dir="./bigWigs",
)

Finally here is the bash to recreate my environment

conda create -n scverse-lite-py39 python=3.9 -y
conda activate scverse-lite-py39
pip install snapatac2

Start with snap.ex.export_coverage and reproduce the failure using the pbmc5k annotated_h5ad tutorial dataset and the environment shown in the report. Compare the bigWig panic with the empty bedgraph output; done means coverage files are written with data instead of raising PanicException or completing empty.