Improvement: Speed up element is leaf test

[Davknapp]

Describe your changes here:
Closes #1646

Adapts the original test to only be parametrized over all schemes, eclasses and a level. The functionality is tree specific and therefore does not need to run over all cmeshes in our testsuite.

Adds a test for a all scheme collections to test if the right function is called in a hybrid forest.

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