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

@@ -3,3 +3,9 @@ set -e
 
 cargo test --locked --package payjoin --verbose --all-features --lib
 cargo test --locked --package payjoin --verbose --all-features --test integration
+
+cargo test --locked --package payjoin --verbose --no-default-features --features v1 --lib
+cargo test --locked --package payjoin --verbose --no-default-features --features v1 --test integration
+
+cargo test --locked --package payjoin --verbose --no-default-features --features v2 --lib
+cargo test --locked --package payjoin --verbose --no-default-features --features v2 --test integration