Support for Go 1.27 UUIDs

[F21]

Is your feature request related to a problem? Please describe.
Go has a uuid package as part of std lib since 1.27 https://pkg.go.dev/uuid
It would be great if pgtype.UUID can return a std lib uuid directly.

Describe the solution you'd like
I am currently updating my projects to remove the google/uuid dependency in favor of the std lib uuid. As the std lib uuid implementation does not include Valuer or Scanner implementations, it is a bit unwieldy to work with when used with pgx results. I need to implement some boiler code to convert the [16]byte into a std lib uuid.

Describe alternatives you've considered
None.

Additional context
None.

[jackc]

Any [16]byte is already supported, including the new uuid.UUID type. But the actual implementation of pgtype.UUID can't change until:

1. Go 1.27 is the minimum supported version by pgx
2. We figure out how to do it without a breaking change or we accept a breaking change