[Backend] Use more efficient .Length/.Count check

[imnasnainaec]

In preparation for updated pragma suggestions with .NET 8.0 in #3046.

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 73.45%. Comparing base (dea7e6c) to head (da7c0fe).

❗ Current head da7c0fe differs from pull request most recent head b6d07cf. Consider uploading reports for the commit b6d07cf to get more accurate results

Files	Patch %	Lines
Backend/Services/StatisticsService.cs	60.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3050      +/-   ##
==========================================
- Coverage   74.29%   73.45%   -0.84%     
==========================================
  Files         269      268       -1     
  Lines       10323    10306      -17     
  Branches     1217     1212       -5     
==========================================
- Hits         7669     7570      -99     
- Misses       2303     2382      +79     
- Partials      351      354       +3     

Flag	Coverage Δ
backend	82.92% <75.00%> (ø)
frontend	64.67% <ø> (-1.64%)	⬇️

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[jasonleenaylor]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)