Write a fast-path for attribute.Set metrics API usage

[jmacd]

Is your feature request related to a problem? Please describe.
The OTel-Go metrics API v0.38 includes functional options to support use of precalculated attribute.Set objects. This will require a separate code path to be as optimized as the existing code path.

Describe the solution you'd like
Fortunately, the existing code structure makes this fairly straightforward. Because synchronous instrument state is aggregated without a uniqueness requirement, that is because synchronous instrument state is allowed to hold multiple copies of the same attribute set, a parallel data structure mapping attribute.Set to *record can be crafted. It will be simpler than the []attribute.KeyValue code path.

Describe alternatives you've considered
#447 installs a slow path workaround.

Additional context
See #446.