Switch to const iterator in EventList

[peterfpeterson]

This is a minor cleanup of the code to use const_iterator when possible and change to range based for loops in a couple of places.

To test:

This is a minor refactor of the code to let the compiler do its thing. All automated tests should pass.

Refs #34794

This does not require release notes because it is an internal refactor.

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Reviewer

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Code Review

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• Are the unit tests small and test the class in isolation?
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Functional Tests

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