Check on Index of data too strict in `statespace`

[AlexAndorra]

As discussed with @jessegrabowski , the statespace module has a check on indices of passed observed data that seems to strict: if you pass an integer Index, it will not accept it because it's technically not a RangeIndex:

a = pd.DataFrame(
    index=np.arange(8), columns=["A", "B", "C", "D"], data=np.arange(32).reshape(8, 4)
)

mod = st.LevelTrendComponent(order=2, innovations_order=[0, 1])
ss_mod = mod.build(name="a")

initial_trend_dims, sigma_trend_dims, P0_dims = (
    ss_mod.param_dims.values()
)
coords = ss_mod.coords

with pm.Model(coords=coords) as model_1:
    P0_diag = pm.Gamma("P0_diag", alpha=5, beta=5)
    P0 = pm.Deterministic("P0", pyt.eye(ss_mod.k_states) * P0_diag, dims=P0_dims)

    initial_trend = pm.Normal("initial_trend", dims=initial_trend_dims)
    sigma_trend = pm.Gamma("sigma_trend", alpha=2, beta=50, dims=sigma_trend_dims)

    ss_mod.build_statespace_graph(
        a["A"],
        mode="JAX",
    )
IndexError: Expected pd.DatetimeIndex or pd.RangeIndex on data, found <class 'pandas.core.indexes.base.Index'>

Maybe the check can be relaxed to non-consecutive integer index?
Also note that even if casting the index above to RangeIndex, the model will throw a warning about not finding a TimeIndex in the data, which I think is expected if you have a RandeIndex already.