Make query planning of index scans fast again

[joka921]

Since #1619, the size estimate for an index scan always involved one or several copies of the block metadata, which incurred a significant query planning cost for most queries. Now, such a copy is only made for an index scan followed by a FILTER and only the metadata of those blocks is copied, which remain after the FILTER (in which case the two operations are expensive anyway).

[sparql-conformance]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=e48f215b724f8607bcdb14a7e3181cc0e2a95935&prev=0400f9076a7cfccc03cda554f423503ce28a5875

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.68%. Comparing base (0400f90) to head (e48f215).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1674   +/-   ##
=======================================
  Coverage   89.67%   89.68%           
=======================================
  Files         383      383           
  Lines       36942    36941    -1     
  Branches     4174     4174           
=======================================
+ Hits        33129    33131    +2     
+ Misses       2512     2511    -1     
+ Partials     1301     1299    -2     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[hannahbast]

1-1 with Johannes + tested it on Wikidata + does the job, thanks a lot!