feat(encode): write the TOML 1.1 output form

Assisted-by: DeepSeek V4.1 Flash

docs/API.md

@@ -145,11 +145,12 @@ variants decode into `LocalDateTime`, `LocalDate` and `LocalTime`, whose
 embedded `time.Time` is normalised to UTC (midnight UTC for a local date, the
 zero date for a local time). Every kind may omit the seconds as of TOML 1.1
 (`07:32`, `1979-05-27T07:32`); such a value carries a zero second, and the
-canonical rendering writes full seconds. There is no implicit conversion
-between the offset and local kinds; assigning one to the other is an error.
-The four types take a bare timestamp and never a quoted string, so a document
-that writes a date-time with quotes does not decode into them, and neither
-`encoding.TextUnmarshaler` nor the embedded `time.Time` changes that.
+encoder writes the seconds only when the value carries them, so a document
+written without seconds comes back without them. There is no implicit
+conversion between the offset and local kinds; assigning one to the other is an
+error. The four types take a bare timestamp and never a quoted string, so a
+document that writes a date-time with quotes does not decode into them, and
+neither `encoding.TextUnmarshaler` nor the embedded `time.Time` changes that.
 
 ### Arrays of tables
 
@@ -426,6 +427,23 @@ carry verbatim (an embedded run of three single quotes, a control character
 other than tab or newline, or a carriage return outside a CRLF pair) also keeps
 the basic form, so the output always re-parses to the same value.
 
+### Inline tables
+
+A table element of a value array is written as one `{a = 1, b = 2}` line while
+it fits. An inline table that would pass the hundredth column carries newlines
+and a trailing comma instead, which TOML 1.1 allows:
+
+```toml
+arr = [1, {
+	n = 1,
+	name = "a value long enough to push the line past the limit",
+}]
+```
+
+The closing brace and the entries are indented one tab per nesting level, a
+nested table is measured on its own line, and the output re-parses to the same
+value either way.
+
 ### Cancellation
 
 `MarshalContext` and `(*Encoder).MarshalContext` accept a `context.Context`. The
@@ -440,6 +458,8 @@ The output is not byte-identical to any document that produced the value:
 - map keys are emitted in sorted order
 - the choice between `[table]` headers and inline tables is not preserved
 - strings use the basic quoted form unless the literal option above applies
+- a date-time drops its zero seconds and the trailing zeros of its fraction, so
+  `07:32:00` is written `07:32`; both are the same value
 - floats always carry a `.` or an exponent, so a float `1` is emitted as `1.0`
   and stays distinguishable from the integer `1` across a round-trip; negative
   zero is normalised to `0.0`
@@ -545,9 +565,11 @@ type LocalDate     struct{ time.Time } // 1979-05-27
 type LocalTime     struct{ time.Time } // 07:32:00.999999
 ```
 
-Each carries a `String()` method returning the TOML-canonical rendering, with
-the fractional second zero-padded to nanosecond precision when present. The
-types are produced by `Parse` and accepted by `Marshal`.
+Each carries a `String()` method returning the TOML-canonical rendering: the
+seconds appear only when the value carries them, and a fractional second drops
+its trailing zeros, so `07:32:00` renders as `07:32` and a half second as
+`00.5`. The types are produced by `Parse` and accepted by `Marshal`, which
+writes them through `String()`.
 
 ## Errors