Small refactorings as preparation for UPDATE queries

[Qup42]

A set of smaller refactoring changes, most of which come from an early proof of concept implementation of SPARQL UPDATE by @hannahbast.
Those include:

• Updating and adding comments in various places.
• Unifying the header formats in various files.
• Making the debug output of ValueIds shorter (V:3 rater than Vocabindex:3).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.79%. Comparing base (0ff6f76) to head (f2a07d2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1353      +/-   ##
==========================================
- Coverage   88.79%   88.79%   -0.01%     
==========================================
  Files         324      324              
  Lines       28650    28653       +3     
  Branches     3170     3171       +1     
==========================================
+ Hits        25441    25442       +1     
- Misses       2060     2062       +2     
  Partials     1149     1149              

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[joka921]

I have a very small suggestion that would be very useful ( a longstanding issue, that can help us with debugging.

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[namedgraph]

"Update queries" are not a thing, they're just "updates" :)