Create functions to perform the remaining difference tests from tern::s_test_proportion_diff():

• prop_cmh() - Stratified Cochran-Mantel-Haenszel test. Internally calls stats::mantelhaen.test().
• prop_schouten() - Chi-Squared test with Schouten correction - relatively rare, not used in any tables

See https://insightsengineering.github.io/tern/latest-tag/reference/h_prop_diff_test.html for details on the tern functions.