add get_interchain: trace a transaction/block to validator blocks + interchain anchors

New transaction.get_interchain and block.get_interchain call the prime-node
/api/v1/{transaction,block}/{id}/interchain endpoints, returning an
InterchainTrace {block_id, validator_blocks, interchain_transactions}. Adds
VerificationBlock / InterchainTransaction / InterchainTrace dataclasses with
from_dict, exports them, and a from_dict test.

prime_sdk/block.py

@@ -1,7 +1,7 @@
 """Block endpoints."""
 
 from .client import Client
-from .models import Block
+from .models import Block, InterchainTrace
 
 
 class BlockClient:
@@ -10,3 +10,11 @@ class BlockClient:
 
     def get(self, block_id: str) -> Block:
         return self._client.get(f"/api/v1/block/{block_id}", Block)
+
+    def get_interchain(self, block_id: str) -> InterchainTrace:
+        """Trace a block to the validator (verification) blocks that validated it
+        and the public-chain interchain anchors those validator blocks were
+        bundled into."""
+        return self._client.get(
+            f"/api/v1/block/{block_id}/interchain", InterchainTrace
+        )