Implement lazy Distinct operation

[RobinTF]

Allow the Distinct operation to deal with lazy inputs.
Note: DISTINCT currently always assumes a sorted input, so the laziness doesn't yet happen too often in practice.

[codecov]

Codecov Report

Attention: Patch coverage is 88.03419% with 14 lines in your changes missing coverage. Please review.

Project coverage is 89.03%. Comparing base (2ccfb50) to head (b63fff2).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
src/engine/Distinct.cpp	87.38%	0 Missing and 14 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1558      +/-   ##
==========================================
- Coverage   89.04%   89.03%   -0.01%     
==========================================
  Files         368      368              
  Lines       33972    34095     +123     
  Branches     3839     3858      +19     
==========================================
+ Hits        30249    30356     +107     
  Misses       2471     2471              
- Partials     1252     1268      +16     

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[joka921]

Initial review on everything but the tests.

[joka921]

I have some small requests

• can you please merge in the current master, s.t. we get a proper Codecov report?

[sparql-conformance]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=b63fff26e207b70f3c46cc0afa0ee9444dab66c2&prev=f9bac20cc250d09a81df657ef5758348ff5779fd

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

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

See analysis details on SonarCloud

[joka921]

The coverage is very hard to track because of te many templates of the callFixedSize optimization.