Add CachedGauge to the registry get / create methods

[coveralls]

Pull Request Test Coverage Report for Build 170

• 16 of 22 (72.73%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.4%) to 89.493%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/measured-core/lib/Collection.js	1	7	14.29%
<!--	Total:	16	22	72.73%	-->

Totals
Change from base Build 168:	-0.4%
Covered Lines:	728
Relevant Lines:	800

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💛 - Coveralls