feat: add ParseAs and NewSchema generics

Assisted-by: GLM 5.3 Flash

docs/API.md

@@ -80,6 +80,23 @@ The one-shot form of a configured `Decoder`: the same options as
 The zero value takes the defaults: unknown keys ignored, numbers evaluated
 as `int64` and `float64`, no size limit and the 10000-level nesting default.
 
+### `func ParseAs[T any](data []byte) (T, error)`
+
+The generic shorthand for `Unmarshal` with a destination variable:
+
+```go
+cfg, err := interpres.ParseAs[Config](data)
+```
+
+The zero `T` comes back with the error.
+
+### `func NewSchema[T any]()`
+
+Precompiles the codec for `T`: the struct schema both directions walk and the
+interface flags the decoder and encoder resolve through are built once and
+cached, so the first document pays the cost instead of the hot path. A `T`
+that is not a struct warms nothing.
+
 ## Documents
 
 `Parse` returns a `Document`: the value tree together with what a map cannot