fix: use ast blocks for simple queries conversions

Fixes cases where {{query nested in BEGIN_* blocks were incorrectly
being converted to queries. Also made ast block handling faster
by only doing one prewalk and cleaned up handling of queries

deps/graph-parser/test/resources/exporter-test-graph/journals/2024_08_07.md

@@ -51,4 +51,9 @@
             [?p :block/name "project"]
             [?b :block/refs ?p]]}
   #+END_QUERY
-  #+END_SRC
+  #+END_SRC
+- Find the blocks containing `tag2` but not `tag1`
+
+  #+BEGIN_EXAMPLE
+  {{query (and [[tag2]] (not [[tag1]]))}}
+  #+END_EXAMPLE