Speckles images issues within example notebook

Discussing with @jenna-tomkinson, the example notebook should be updated for the nuclear speckles dataset to only display filename columns which can display images from the testing dataset.

E.g.

```python
%%time
# view nuclear speckles data with images and overlaid outlines from masks
CytoDataFrame(
data=f"{nuclear_speckles_path}/test_slide1_converted.parquet",
data_context_dir=f"{nuclear_speckles_path}/images/plate1",
data_mask_context_dir=f"{nuclear_speckles_path}/masks/plate1",
)[
[
"Metadata_ImageNumber",
"Nuclei_Number_Object_Number",
"Image_FileName_A647",
"Image_FileName_DAPI",
"Image_FileName_GOLD",
]
][:3]
```

To:

```python
%%time
# view nuclear speckles data with images and overlaid outlines from masks
CytoDataFrame(
data=f"{nuclear_speckles_path}/test_slide1_converted.parquet",
data_context_dir=f"{nuclear_speckles_path}/images/plate1",
data_mask_context_dir=f"{nuclear_speckles_path}/masks/plate1",
)[
[
"Metadata_ImageNumber",
"Nuclei_Number_Object_Number",
"Image_FileName_DAPI",
]
][:3]
```