fix: improve f3 snapshot import performance with batching

[hanabi1224]

This PR improves performance of ImportSnapshotToDatastore by

• changing ds datastore.Datastore to ds datastore.Batching
• using autobatch internally

Stats,
Loading a ~300MiB Filecoin calibnet F3 snapshot on my laptop takes

• ~5s into a memory blockstore
• 30min+ into leveldb without batching
• ~12s into leveldb with batching

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.08%. Comparing base (38f1620) to head (76a0430).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1046      +/-   ##
==========================================
+ Coverage   64.75%   65.08%   +0.33%     
==========================================
  Files          81       81              
  Lines        9894     9896       +2     
==========================================
+ Hits         6407     6441      +34     
+ Misses       2966     2933      -33     
- Partials      521      522       +1     

Files with missing lines	Coverage Δ
certstore/snapshot.go	47.82% <100.00%> (+0.92%)	⬆️

... and 6 files with indirect coverage changes

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