docs(architecture): scope the no-caching claim to the parser

Assisted-by: GLM 5.3 Flash

docs/ARCHITECTURE.md

@@ -99,8 +99,8 @@ sequenceDiagram
   `Decode`, `DecodeContext`, `Marshal` and `MarshalContext` call allocates its
   own unexported worker, so a configured type is safe for concurrent use; the
   setter methods are not, and must finish before the value is shared.
-- The parser is allocated per `ParseContext` call; nothing is cached between
-  documents.
+- The parser is allocated per `ParseContext` call; the parser itself caches
+  nothing between documents.
 - The one piece of shared state is the struct-schema cache in `decode.go`: a
   `sync.Map` keyed by `reflect.Type`, holding the flattened field layout the
   decoder and the encoder both consult. A schema is immutable once published,