Minor performance improvements on hot code paths

[bkoelman]

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• N/A: Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.19%. Comparing base (c0faae3) to head (5fde484).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...otNetCore/Queries/Parsing/QueryExpressionParser.cs	77.77%	1 Missing and 1 partial ⚠️
...DotNetCore/Serialization/Response/JsonApiWriter.cs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1947      +/-   ##
==========================================
- Coverage   92.21%   92.19%   -0.03%     
==========================================
  Files         437      437              
  Lines       14927    14925       -2     
  Branches     2474     2476       +2     
==========================================
- Hits        13765    13760       -5     
- Misses        714      715       +1     
- Partials      448      450       +2     

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