test: Make metric validation more consistent

[chynesNR]

A common source of intermittent integration test failures are cases where we're looking for multiple occurrences of a metric, since there's always a small chance that they fall over more than one harvest cycle. I used a regex to find all of the cases where we're looking for multiple instances, and changed them to check all harvests.

This touched a lot of files but only contains two changes:

1. Replacing callCount with CallCountAllHarvests where appropriate
2. Fixed a bug in TryFindMetrics() (which broke on regex scope assertions that encountered a null scope)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.31%. Comparing base (a77919e) to head (ed8f8dd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2840   +/-   ##
=======================================
  Coverage   81.31%   81.31%           
=======================================
  Files         460      460           
  Lines       29239    29239           
  Branches     3231     3231           
=======================================
  Hits        23777    23777           
  Misses       4669     4669           
  Partials      793      793           

Flag	Coverage Δ
Agent	82.22% <ø> (ø)
Profiler	73.33% <ø> (ø)

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