expose batched sampling option; error handling

[janfb]

fixes #1320

• exposes use_batched_sampling in run_tarp
• catch AssertianError raised in MCMCPosterior when using batched sampling with something else than slice_np_vectorized
• add warning when sampling for a batch of x without batched sampling.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.65%. Comparing base (3bd8aa9) to head (4c69fa4).
Report is 4 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1321       +/-   ##
===========================================
- Coverage   89.39%   78.65%   -10.74%     
===========================================
  Files         118      118               
  Lines        8709     8722       +13     
===========================================
- Hits         7785     6860      -925     
- Misses        924     1862      +938     

Flag	Coverage Δ
unittests	78.65% <100.00%> (-10.74%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sbi/diagnostics/sbc.py	95.71% <ø> (ø)
sbi/diagnostics/tarp.py	82.92% <ø> (-14.64%)	⬇️
sbi/utils/diagnostics_utils.py	100.00% <100.00%> (+4.00%)	⬆️

... and 31 files with indirect coverage changes

[michaeldeistler]

LGTM, thanks!