feat: add OffsetDateTime, nesting limits and uniform Marshaler dispatch

Assisted-by: DeepSeek V4.1 Flash

CHANGELOG.md

@@ -28,6 +28,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   at most `threshold` bytes is written as an inline table instead of a header
   section, which shortens a document of small tables. An array of tables keeps
   its header form, because its inline form would re-parse as a value array.
+- `OffsetDateTime`, the Go type of the offset date-time kind, so that all four
+  TOML date-time kinds have one of their own. `Parse` and `Unmarshal` hand it
+  back where they produced a bare `time.Time` before, and `Marshal` accepts it.
+  Unmarshalling into a struct field of type `time.Time` keeps working, because
+  the plain type takes an offset date-time as it always did; code that asserts
+  the tree's type, and `UnmarshalTOML` implementations that expect a
+  `time.Time`, need the new type.
+- `Decoder.MaxDepth(depth)` and `Decoder.MaxInputSize(size)` bound the parse a
+  `Decode` performs, and every parse carries a nesting limit in any case
+  (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.
 
 ### Changed
 
@@ -40,6 +52,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - An inline table that would pass the hundredth column is written across lines
   with a trailing comma and one tab of indentation per nesting level, the shape
   TOML 1.1 allows an inline table to take.
+- `MarshalTOML` reaches every array element and every field, whatever the Go
+  kind, and its result is normalised like any other value: an element rendering
+  itself as a table keeps the `[[header]]` form, one rendering itself as a
+  scalar turns the array into a value array, and the method runs once per
+  element. It is found on the addressable pointer as well, so a
+  pointer-receiver `MarshalTOML` is called for a field or an element, exactly
+  as `MarshalText` is.
 - TOML 1.1 is the acceptance contract, and TOML 1.0 is not. The compliance
   suite runs the 1.1 corpus alone, and the promise that every 1.0 document
   parses exactly as before is withdrawn. Nothing that parses today stops