Avoid multiple component registrations

[rmorshea]

Since one can use the same component more than once we should avoid calling _register_component more than once if it's already been done. A simple containment check in IDOM_REGISTERED_COMPONENTS should work here.

[Archmonger]

Accidentally commented on the wrong issue before, so I'm reposting here

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Caching the register function with functools.cache would provide the same ability to skip re-registration, and would allow us to skip the sys.modules check. Could be slightly more performant than checking IDOM_REGISTERED_COMPONENTS.

[Archmonger]

Note: recently discovered there is no performance penalty for importing a module more than one time. Apparently importlib already does a sys.modules check. Which means we can remove this LOC.

See here for more details.