GetInterchain: perChain + chains options (default first anchor per chain)

Transaction.GetInterchain and Block.GetInterchain take variadic options
(client.WithPerChain / client.WithChains, re-exported as sdk.WithPerChain /
sdk.WithChains) that map to the new prime-node ?perChain=&chains= query params.
Backward compatible: existing no-option calls get the default (one anchor per
chain). client.InterchainQuery builds the suffix; unit-tested.

transaction/transaction.go

@@ -56,9 +56,14 @@ func (tc *TransactionClient) Get(ctx context.Context, transactionID string) (*mo
 // validated its prime block and the public-chain interchain anchors those
 // validator blocks were bundled into. If the transaction is still pending (not
 // yet in a block) the trace's slices are empty.
-func (tc *TransactionClient) GetInterchain(ctx context.Context, transactionID string) (*models.InterchainTrace, error) {
+//
+// By default it returns the first anchor per public chain (anchor proofs are
+// chained, so the earliest per chain is the meaningful one). Use
+// client.WithPerChain / client.WithChains to return more anchors per chain or
+// restrict to specific chains.
+func (tc *TransactionClient) GetInterchain(ctx context.Context, transactionID string, opts ...client.InterchainOption) (*models.InterchainTrace, error) {
 	var resp models.InterchainTrace
-	path := fmt.Sprintf("/api/v1/transaction/%s/interchain", transactionID)
+	path := fmt.Sprintf("/api/v1/transaction/%s/interchain%s", transactionID, client.InterchainQuery(opts...))
 	err := tc.client.Get(ctx, path, &resp)
 	if err != nil {
 		return nil, err