feat!: rework the public API to json/v2-style variadic options

Assisted-by: GLM 5.3 Flash

README.md

@@ -15,7 +15,7 @@ the entire official [toml-test](https://github.com/toml-lang/toml-test) suite:
   optional as of 1.1; arrays and inline tables, multi-line as of 1.1.
 - **Decoding and encoding**: `Parse` for an untyped tree, `Unmarshal` and
   `Marshal` for structs and maps, mirroring `encoding/json`.
-- **Strict decoding**: `NewDecoder().DisallowUnknownFields()` rejects keys that
+- **Strict decoding**: `RejectUnknownFields(true)` rejects keys that
   match no destination field, at every struct depth.
 - **Custom types**: `Marshaler` and `Unmarshaler` let a type control its own
   TOML representation in both directions, and `encoding.TextMarshaler` and
@@ -101,9 +101,7 @@ which is the layout that re-parses to the same tree.
 ### Strict decoding
 
 ```go
-err := interpres.NewDecoder().
-	DisallowUnknownFields().
-	Decode(data, &cfg)
+err := interpres.Unmarshal(data, &cfg, interpres.RejectUnknownFields(true))
 ```
 
 A key with no matching field becomes an error instead of a silent drop.
@@ -132,16 +130,20 @@ func (ip *IP) UnmarshalTOML(data any) error {
 The value `MarshalTOML` returns is encoded in place of the receiver;
 `UnmarshalTOML` receives the parsed value verbatim.
 
-### Encoder options
+### Options
 
 ```go
-out, err := interpres.NewEncoder().
-	Layout(interpres.LayoutKindDeclaration), // preserve declaration order
-	OmitEmptyArrays().       // skip empty scalar arrays
-	LiteralMultiline(80),       // long multi-line strings as literal blocks
-	Marshal(cfg)
+out, err := interpres.Marshal(cfg,
+	interpres.Layout(interpres.LayoutKindDeclaration), // preserve declaration order
+	interpres.OmitEmptyArrays(true),       // skip empty scalar arrays
+	interpres.LiteralMultiline(80),        // long multi-line strings as literal blocks
+)
 ```
 
+The decode and encode calls take variadic options, the shape
+encoding/json/v2 uses for its own. `UnmarshalRead(r, v, opts...)` and
+`MarshalWrite(w, v, opts...)` are the streaming forms.
+
 ### Cancellation
 
 ```go
@@ -151,8 +153,7 @@ defer cancel()
 out, err := interpres.MarshalContext(ctx, cfg)
 ```
 
-`ParseContext`, `UnmarshalContext`, `(*Decoder).DecodeContext` and
-`(*Encoder).MarshalContext` follow the same pattern.
+`ParseContext`, `UnmarshalContext` and `MarshalContext` follow the same pattern.
 
 The full rules for field matching, numeric conversion and emission live in
 [docs/API.md](docs/API.md).