feat: add early prefix check in inverse queries

Before parsing each key, verify that it still matches the seek prefix.
This avoids iterating through keys that are lexicographically close but
cannot match. This significantly improves performance for queries for
non-existent prefixes that have many shorter prefix matches in the
database.

Author: satta

backend/balboa-rocksdb/rocksdb-impl.c

@@ -1,5 +1,5 @@
 // balboa
-// Copyright (c) 2018, 2019 DCSO GmbH
+// Copyright (c) 2018, 2026 DCSO GmbH
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -467,6 +467,10 @@ static int blb_rocksdb_query_by_i(
     keys_visited += 1;
     size_t key_len = 0;
     const char* key = rocksdb_iter_key(it, &key_len);
+    if(key_len < prefix_len
+       || memcmp(key, dbc->scrtch_inv, prefix_len) != 0) {
+      break;
+    }
     char* err = NULL;
 
     enum TokIdx { RDATA = 3, SENSORID = 2, RRNAME = 1, RRTYPE = 0, FIELDS = 4 };