[TSDB] fingerprint offsets is now correctly 16 byte aligned

[owen-d]

This contains a few fixes I've found over the past few days of debugging TSDB operations (sorry for being all over the place), but the important bits are

1. Correctly calculates storage.SeriesRef offsets in the fingerprintOffsets table in 7a34b15. This resulted in an incredibly hard to find bug in sharding code because it wasn't:
   • Using section offsets to increase the starting offsets for our series references
   • Using 16 byte offsets of the file position not series number

It caused everything but the last shard to be skipped most off the time because the actual references were waaay higher than expected
2) Simplifies the query planning algorithm to consistently prefer smaller units of work.

ref #5428

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0.6%

[cyriltovena]

LGTM