Pass refs to extension functions

[john-h-kastner-aws]

Description of changes

A slightly more involved follow-up to #1398. Updates extension functions to take arguments by reference instead of by value. In the current code, extension function arguments start as a slice before the elements are unconditionally cloned and passed to the definition of the function. With this PR we now pass references to the extension function which may or may not clone the argument values.

I've also made the Duration and DateTime structs Copy since they are wrappers around i64s and updated function signatures using these types to take owned values rather than references based on clippy's recommendation.

Issue #, if available

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The change in this PR is (choose one, and delete the other options):

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