Add ARD functions for proportion difference estimation

[edelarua]

Create functions to estimate proportion differences from tern::s_test_proportion_diff():

• prop_diff_wald()
• prop_diff_ha()
• prop_diff_nc()
• prop_diff_cmh()
• prop_diff_strat_nc()

First double check whether any of these are already possible with current cardx functions, and whether the results match those from the tern functions, which all use custom calculation function desctools_binom() to return results.

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