cats.mtl.Local[IO, E] from IOLocal[E]

[rossabaker]

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cats.mtl.Local's semantics are a safe and useful subset of what can be done with IOLocal. This provides easy access to a Local[F, E] instance from an IOLocal[E] value.

• core takes on a cats-mtl dependency. Note that testkit already couples these release cycles.
• Adds IOLocal#asLocal to get a Local view of an IOLocal value
• Adds IOLocal.local to create an IOLocal and return a local view of it, inside IO.

A similar view is already in use in otel4s.

Fixes #3385.