Standardize test messages to use the permissible constraints (i.e. the thing being asserted)

[ccaprani]

Following on from the discussion here pymc-devs/pymc-extras#84 (comment) with @ricardoV94, in many places the test message is written in the opposite direction to the check it looks like, e.g. Gumbel, Logistic, Normal, HalfNormal, Beta; e.g.

check_parameters(res, 0 < beta, msg="beta > 0")

Others are written in the same direction, e.g. TruncatedNormal, Wald, Kumaraswamy and so on.

logp = check_parameters(
                logp,
                at.le(lower, upper),
                msg="lower_bound <= upper_bound",
            )

Messages should be standardized to use the permissable constraints; i.e. written in the same direction.

[ricardoV94]

That first example is fine, the expression is the same just written the other way around. The problem is if it has the opposite meaning

[ricardoV94]

Closed via #6272