TST: anova with `-1` noconstant, add tests

adds unit test for noconstant case for ANOVA

issue #1213 looks outdated, results in examples are the same as in R without changes

where/when was this fixed

AFAIU: `df_model` doesn't know anything about a constant
obviously it does now take implicit constants into account see last comment in #1213 


That's the point, the degrees of freedom difference for the test only depends on the number of parameters and is independent of whether one of them is a constant or not, which would be in df_resid.
In constrast, df_model excludes the constant if we can identify hasconst=1.  (so we need to watch out that we count all parameters.  (df_model + hasconst)_modelA - (df_model + hasconst)_modelB

what I'm not sure about:
how does it work for the first comparison with "no regressors" at all if there is no constant. Given that it's an f_test it would be just that all coefficients are zero, including the constant if there is a constant.
This still assumes that we have a nested sequence of models, so either they all have an explicit or implicit constant or none of them does.

(aside: penalized models have fractional df_resid, but df_model should be adjusted accordingly, so it doesn't add any additional problems)