No std bytes writer

[Person-93]

This is part of the WIP no_std support.

I've made impl of std::io::Write for PyBytesWriter conditional on wip_feature_std. This makes PyBytesWriter completely useless without the std feature, so I've added an additional method write_bytes.

[bschoenmaeckers]

We currently do not expose PyBytesWriter directly. So adding an extra method is not usable right now.

The only usage is a dyn Write ref passed here:

pyo3/src/types/bytes.rs

Lines 160 to 171 in d5daa3d

	pub fn new_with_writer<F>(
	py: Python<'_>,
	reserved_capacity: usize,
	write: F,
	) -> PyResult<Bound<'_, PyBytes>>
	where
	F: FnOnce(&mut dyn Write) -> PyResult<()>,
	{
	let mut writer = PyBytesWriter::with_capacity(py, reserved_capacity)?;
	write(&mut writer)?;
	writer.try_into()
	}

Should we expose PyBytesWriter directly or disable it completely until core has io::Write?

[Person-93]

Should we expose PyBytesWriter directly or disable it completely until core has io::Write?

I think it makes sense to expose it directly in that function.