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.

prime_sdk/interchain.py

@@ -0,0 +1,27 @@
+"""Query builder for the interchain-trace endpoints.
+
+Anchor proofs are chained, so by default the trace returns the first anchor per
+public chain; these options change how many and which chains are returned.
+"""
+
+from typing import List, Optional
+from urllib.parse import quote
+
+
+def interchain_query(
+    per_chain: Optional[int] = None, chains: Optional[List[str]] = None
+) -> str:
+    """Build the "?perChain=...&chains=..." suffix for the interchain trace
+    endpoints.
+
+    Returns "" when nothing is set (the server then applies its defaults: one
+    anchor per chain, all chains). ``per_chain`` caps anchors per public chain,
+    earliest-first (1 = first per chain; 0 = all). ``chains`` restricts to the
+    given chain ids ("1" = ETH mainnet, "0" = BTC; testnet ids differ).
+    """
+    parts: List[str] = []
+    if per_chain is not None:
+        parts.append(f"perChain={int(per_chain)}")
+    if chains:
+        parts.append("chains=" + ",".join(quote(str(c), safe="") for c in chains))
+    return "?" + "&".join(parts) if parts else ""