Add test suite for v1 and v2 specific features alone

Add the test suite for the `contrib/test,sh` script in the payjoin
crate.

Author: benalleng

payjoin/contrib/test.sh

@@ -1,5 +1,12 @@
 #!/usr/bin/env bash
 set -e
 
+features=("v1" "v2")
+
 cargo test --locked --package payjoin --verbose --all-features --lib
 cargo test --locked --package payjoin --verbose --all-features --test integration
+
+for feature in "${features[@]}"; do
+  cargo test --locked --package payjoin --verbose --no-default-features --features "$feature" --lib
+  cargo test --locked --package payjoin --verbose --no-default-features --features "$feature" --test integration
+done