Unit tests for delegator factories

[boesing]

Since we now reverted the bug which was introduced in 3.3.1 and fixed in 3.3.2, unit tests which do actually test if delegator factories are being applied to the services fetched via the laminas-servicemanager would be very helpful.

Ofc, these might break in the next major when we cleanup the current behavior but until then, we should try to avoid having this same issue again in this (and maybe in other repositories).

Reverted in #100

Originally posted by @Ocramius in #99 (comment)

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Maybe this could also be a CommonPluginManagerTrait test - so actually finding "dead" delegators.

But in the first place, we should ensure that delegator factories are actually be used within the servicemanager.

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References #99