feat: decode arrays into [N]T and add MarshalAppend

Assisted-by: GLM 5.3 Flash

CHANGELOG.md

@@ -46,6 +46,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   (10000 levels, which no hand-written document approaches): a document that
   nests arrays or inline tables deeper used to run the stack out and is now
   rejected with a `SyntaxError` naming the limit.
+- A TOML array decodes into a Go fixed-size array, `[N]T`, where only a slice
+  was accepted before; the encoder could already encode one. A length mismatch
+  is an error wrapped with the key path.
+- `MarshalAppend(buf, v)` appends the TOML encoding of v to buf and returns
+  the extended buffer, the shape `json.MarshalAppend` has.
 - `ParseFile(path)` reads the file and parses it into a `Document`, with the
   file name at the front of every error it returns, read failure and parse
   failure alike. `Valid(data)` reports whether a document parses, nil on