Add builtin function ql:toEpoch

[yarox-1]

This adds the function ql:toEpoch. With this a xsd:datetime can be turned into an epoch timepoint in int. This function allows to correcly use =, <, > for xsd:datetime objects.

Here is an example for =:

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT ?date1 ?date2 ?neqWithoutEpoch ?eqWithEpoch 
WHERE {
     BIND("2025-12-24T18:15:00Z"^^xsd:dateTime AS ?date1)
     BIND("2025-12-24T17:15:00-01:00"^^xsd:dateTime AS ?date2)
     BIND(?date1 = ?date2 AS ?neqWithoutEpoch)
     BIND(ql:toEpoch(?date1) = ql:toEpoch(?date2) AS ?eqWithEpoch)
}

and here for <:

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT ?date1 ?date2 ?lt1 ?lt2
WHERE {
    BIND("2025-12-24T14:15:00Z"^^xsd:dateTime AS ?date1)
    BIND("2025-12-24T13:15:00-02:00"^^xsd:dateTime AS ?date2)
    BIND(ql:toEpoch(?date1) < ql:toEpoch(?date2) AS ?lt1)
    BIND(ql:toEpoch(?date2) < ql:toEpoch(?date1) AS ?lt2)
}

[codecov]

Codecov Report

❌ Patch coverage is 57.69231% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.34%. Comparing base (eeb9fd0) to head (4105ab0).
⚠️ Report is 13 commits behind head on master.

Files with missing lines	Patch %	Lines
src/engine/sparqlExpressions/DateExpressions.cpp	15.38%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2841      +/-   ##
==========================================
- Coverage   92.38%   92.34%   -0.04%     
==========================================
  Files         506      510       +4     
  Lines       43998    44139     +141     
  Branches     5824     5836      +12     
==========================================
+ Hits        40649    40762     +113     
- Misses       1697     1715      +18     
- Partials     1652     1662      +10     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ullingerc]

Thank you very much, this is a very useful function.
I have pointed out two minor details, otherwise this is good to go.

[sparql-conformance]

Overview

Number of Tests	Passed ✅	Intended ✅	Failed ❌	Not tested
548	447	73	28	0

Conformance check passed ✅

No test result changes.

Details: https://qlever.dev/sparql-conformance-ui?cur=4105ab0c10a6564e99831cb4ab3b57ea33f96a54&prev=f54b0a34f8d91af3bbdb7dbc32f115d295e11c31

[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