add `ard_svychisq()` function #176

All 21 tests pass, 9 skipped in 5s

1 files ±0 31 suites ±0 5s ⏱️ -1s
30 tests ±0 21 ✅ ±0 9 💤 ±0 0 ❌ ±0
74 runs ±0 54 ✅ ±0 20 💤 ±0 0 ❌ ±0

Results for commit ea322f6. ± Comparison against earlier commit 11fce38.