Add filter_per_worker flag to data loaders

[rusty1s]

If wished, PyG data loaders can now execute the filtering of data according to samples in the worker process. This eases integration with out-of-memory feature stores.

[codecov]

Codecov Report

Merging #4873 (128bba7) into master (927346e) will decrease coverage by 0.01%.
The diff coverage is 82.35%.

@@            Coverage Diff             @@
##           master    #4873      +/-   ##
==========================================
- Coverage   82.77%   82.76%   -0.02%     
==========================================
  Files         329      329              
  Lines       17679    17703      +24     
==========================================
+ Hits        14634    14652      +18     
- Misses       3045     3051       +6     

Impacted Files	Coverage Δ
torch_geometric/loader/hgt_loader.py	90.56% <81.81%> (-2.77%)	⬇️
torch_geometric/loader/link_neighbor_loader.py	92.08% <81.81%> (-1.05%)	⬇️
torch_geometric/loader/neighbor_loader.py	86.12% <81.81%> (-0.54%)	⬇️
torch_geometric/loader/base.py	78.57% <100.00%> (ø)

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[mananshah99]

LGTM, thank you!