There are some published Stereo-seq 3D data in GEO: GSE278603. The http link
for the file is https://www.ncbi.nlm.nih.gov/geo/download/?acc=GSE278603&format=file.
It contains 6 anndata files, with 3 timepoints (E7.5, E7.75 and E8.0) and 2 replicates (rep1 and rep2).
I want you to:

1. Download the data and visualize all 6 anndata object it in 3D space in a single figure.
2. As a showcase, use E8.0 rep2 data to identify spatially variable genes (SVGs) and plot the spatial expression patterns of top 3 SVGs.
3. Use rep2 data of three timepoints to create a UMAP, identify the temporal variable genes (TVGs) and show the temporal expression patterns of top 3 TVGs on the UMAP space.
4. Use rep2 data of three timepoints to create a cell type transition figure across timepoints. This might requires implementing optimal transport across timepoints. You can subsample the data for this step to speed up the analysis.