Making `ard_survey_svycontinuous()` a S3 method #43

All 44 tests pass, 21 skipped in 10s

1 files ± 0 65 suites +8 10s ⏱️ +2s
65 tests + 8 44 ✅ + 5 21 💤 +3 0 ❌ ±0
182 runs +34 149 ✅ +30 33 💤 +4 0 ❌ ±0

Results for commit aa56368. ± Comparison against earlier commit 5c55508.