Make EventCounterAlg reentrant

Motivated by @ishapova's presentation at yesterday's Core Software meeting. The updated code is (was) essentially a copy of the Gaudi's [EventCounter]((https://gitlab.cern.ch/gaudi/Gaudi/-/blob/199b5287a7e024ab7ac11556ebaca2f9014dfd7f/GaudiAlg/src/lib/EventCounter.cpp).

This merge request affects 2 packages:

• Control/GaudiSequencer
• Reconstruction/RecExample/RecExCommon

Affected files list will not be printed in this case

Adding @goetz ,@ssnyder as watchers

added Core Reconstruction master review-pending-level-1 labels

CI Result SUCCESS (hash 4ccf5cc9)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis	DetCommon
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthAnalysis: number of compilation errors 0, warnings 0
DetCommon: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 30708]

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 6b7b8018

added sweep:ignore label