remote-test: use u64 to represent file size
Currently, triggering a transfer of data exceeding the size of 4294967295 bytes results in a panic on the `remote-test-server` as `io::copy(&mut file, dst) failed with Connection reset by peer (os error 104)`. This issue happens because the size is transmitted as u32 to `remote-test-server`.
First commit increases the supported file size. But I am not sure about its necessity — can we realistically encounter file sizes exceeding 4GB in builds, perhaps through some complicated configurations?
~The second commit adds a sanity check to avoid encountering the error `io::copy(&mut file, dst) failed with Connection reset by peer (os error 104)` on the `remote-test-server` side.~
9e896f42bd