matchednull - Matched-Null Tests for Cluster-Count Claims

Builds matched nulls for cluster-count claims: synthetic twins of a dataset that preserve every marginal distribution and the full correlation matrix while containing no cluster structure by construction. A reported number of clusters or "types" can then be tested against what the data's own margins and covariance already produce, using any clustering pipeline. A t-copula option adds tail dependence to the null, so that an apparent excess of clusters can be checked against a heavier-tailed alternative before it is read as evidence of types. Implements the matched-null procedure of Meng (2026) "Types Without Taxa" <https://osf.io/2ekcg>.