get_interchain: per_chain + chains options (default first anchor per chain); bump 0.5.0

transaction.get_interchain / block.get_interchain take per_chain= and chains=
kwargs mapping to prime-node's ?perChain=&chains= params. Default (no kwargs)
returns one anchor per chain. Shared interchain_query() helper, exported; pytest.

tests/test_interchain.py

@@ -0,0 +1,22 @@
+"""Offline tests for the interchain-trace query builder."""
+
+from prime_sdk import interchain_query
+
+
+def test_empty_when_nothing_set():
+    assert interchain_query() == ""
+    assert interchain_query(None, None) == ""
+    assert interchain_query(chains=[]) == ""
+
+
+def test_per_chain_including_zero():
+    assert interchain_query(per_chain=1) == "?perChain=1"
+    assert interchain_query(per_chain=0) == "?perChain=0"
+
+
+def test_chains_joined_with_commas():
+    assert interchain_query(chains=["1", "0"]) == "?chains=1,0"
+
+
+def test_combined():
+    assert interchain_query(per_chain=2, chains=["1", "0"]) == "?perChain=2&chains=1,0"