Upgrade and improve Uniquifier API

[mkorbel1]

Description & Motivation

The Uniquifier in ROHD is useful in many situations, but not exposed as a public API of ROHD (yet?). Because it is private, the API is a little bit confusing as it relates to reserved items and was also not heavily unit tested.

This PR:

• Adds better testing for the Uniquifier
• Upgrades the isAvailable API to properly consider whether a reserved item should be considered available or not
• Optimizes the implementation to be a little more performant, since it is called many times

Related Issue(s)

Related to #134, but not closing it

Testing

Added new tests, and existing tests help protect that nothing broke

Backwards-compatibility

Is this a breaking change that will not be backwards-compatible? If yes, how so?

Only if someone relied on the weird API behavior of an internal utility of ROHD

Documentation

Does the change require any updates to documentation? If so, where? Are they included?

No