Properly differentiate between cancelled and failed for lazy results

[RobinTF]

This makes it consistent that lazily generated results also get the proper cancelled status when the operation was cancelled.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.52%. Comparing base (89e524b) to head (dd003f3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2628   +/-   ##
=======================================
  Coverage   91.52%   91.52%           
=======================================
  Files         478      478           
  Lines       40951    40964   +13     
  Branches     5443     5445    +2     
=======================================
+ Hits        37479    37493   +14     
  Misses       1900     1900           
+ Partials     1572     1571    -1     

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[sparql-conformance]

Overview

Number of Tests	Passed ✅	Intended ✅	Failed ❌	Not tested
544	447	73	24	0

Conformance check passed ✅

Test Status Changes 📊

Number of Tests	Previous Status	Current Status
6	-	Intended
6	-	Failed
7	-	Passed

Details: https://qlever.dev/sparql-conformance-ui?cur=dd003f3b29e7649f33ea3944d33141ae089927e6&prev=89e524b99fec2866ac9d20409da2e2d6d70fd98e

[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 SonarQube Cloud