docs: align the remaining Decoder and Encoder mentions with the options API

Assisted-by: GLM 5.3 Flash

docs/ARCHITECTURE.md

@@ -35,7 +35,7 @@ strict validation.
 
 | Path | Responsibility |
 |---|---|
-| `.` (package `interpres`) | The whole library. `interpres.go` declares the exported surface (`Parse`, `Unmarshal`, `Marshal`, the `*Context` variants, `Decoder`, `Encoder`, `Marshaler`, `Unmarshaler`, `SyntaxError`, the local date-time types); everything below it is unexported. |
+| `.` (package `interpres`) | The whole library. `interpres.go` declares the exported surface (`Parse`, `Unmarshal`, `Marshal`, the `*Context` variants, the option constructors, `Marshaler`, `Unmarshaler`, `SyntaxError`, the local date-time types); everything below it is unexported. |
 | `cmd/interpres-decode` | The toml-test adapter, both directions. Reads TOML on stdin, writes tagged JSON on stdout; with `-encode` it reads tagged JSON and writes TOML. Owns no parsing logic and no emission logic. |
 | `examples/basic` | A runnable tour of the API. Documentation in executable form, not part of the library. |
 
@@ -96,10 +96,9 @@ sequenceDiagram
 
 ## State and lifetime
 
-- The exported `Decoder` and `Encoder` hold configuration only. Every
-  `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 option values are stateless: every `Unmarshal`, `Marshal` and their
+  variants apply their own options into a per-call unexported worker, so the
+  entries are safe for concurrent use.
 - The parser is allocated per `ParseContext` call; the parser itself caches
   nothing between documents.
 - The shared state is a set of caches and pools whose entries are immutable