Support an immediate read as part of `open_object()`

[coryan]

It is possible to both open an object and then read some data. Maybe do something like:

// Open and read the trailer...
let (descriptor, reader) = client.open_object("...bucket", "my-object.parquet").send_with_read(ReadRange::last(32)).await?;

// ^^^ that has lower latency than the following:
let descriptor = client.open_object("...bucket", "my-object.parquet").send().await?;
let reader = descriptor.read_range(ReadRange::last(32)).await;

I think we can support this in the client and request builders "easily", but it may affect the mocks and therefore we should at least design for it before releasing this thing.

[coryan]

I am going to move this to a future improvement. We can add a new open_and_read_object() method to the stubs to make such an addition backwards compatible.