Better frozen params behavior

Rather than freezing the underlying store, let's freeze values when
accessed.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Don't freeze params

While immutability is generally a good thing, Ruby just doesn't like it,
and neither do its popular libraries.

We can revisit this in the future, but for now it makes things too
brittle.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>