feat: add Error associated type in zio::Ops to handle multiple errors

[CosminPerRam]

Ops::run and Ops::run_vec return Result<Status, DecompressError>.
There are 2 implementations of it, in Decompress which everything is all good, and in Compress, which because of the trait, results in the usage of some .unwrap()'s:

flate2-rs/src/zio.rs

Lines 40 to 47 in 5c6eaec

	fn run(
	&mut self,
	input: &[u8],
	output: &mut [u8],
	flush: FlushCompress,
	) -> Result<Status, DecompressError> {
	Ok(self.compress(input, output, flush).unwrap())
	}

and

flate2-rs/src/zio.rs

Lines 48 to 55 in 5c6eaec

	fn run_vec(
	&mut self,
	input: &[u8],
	output: &mut Vec<u8>,
	flush: FlushCompress,
	) -> Result<Status, DecompressError> {
	Ok(self.compress_vec(input, output, flush).unwrap())
	}

So, adding an associated type in Ops covers both.
Because of this, these unwraps are also handled now:

flate2-rs/src/zio.rs

Lines 255 to 277 in 5c6eaec

	fn flush(&mut self) -> io::Result<()> {
	self.data
	.run_vec(&[], &mut self.buf, D::Flush::sync())
	.unwrap();
	// Unfortunately miniz doesn't actually tell us when we're done with
	// pulling out all the data from the internal stream. To remedy this we
	// have to continually ask the stream for more memory until it doesn't
	// give us a chunk of memory the same size as our own internal buffer,
	// at which point we assume it's reached the end.
	loop {
	self.dump()?;
	let before = self.data.total_out();
	self.data
	.run_vec(&[], &mut self.buf, D::Flush::none())
	.unwrap();
	if before == self.data.total_out() {
	break;
	}
	}
	self.obj.as_mut().unwrap().flush()
	}

(without the last one, that's here for context)
The trait is used only internally, so no breaking changes and only less possible panics (:

[Byron]

That's a great catch, along with a great solution!
Thanks so much!