perf: remove flush from ser::into_writer.

When serializing many records into a writer, it is advantageous to
batch the writes when persisting to a disk or transmitting them over a
socket. The current implementation of `into_writer()` flushes the
encoder after every call which, in turn, flushes the underlying
writer.

This commit removes the flush from the call to `into_writer()`
allowing the programmer to take advantage of tools like
`std::io::BufWriter`.

I was concerned that the encoder could maintain some state that would
be lost if it was dropped before a flush, however, I do not believe
this to be the case because the `Encoder` type is a simple wrapper
around a type implementing the `Write` trait, and the invocation of
`flush()` is on that inner type rather than on anything in the encoder
itself. Therefore call to flush cannot affect the `Encoder` in any
way.

Signed-off-by: John VanEnk <[email protected]>

ciborium/src/ser/mod.rs

@@ -495,6 +495,5 @@ where
     W::Error: core::fmt::Debug,
 {
     let mut encoder = Serializer::from(writer);
-    value.serialize(&mut encoder)?;
-    Ok(encoder.0.flush()?)
+    value.serialize(&mut encoder)
 }