Prevent Partial Reads and Writes

See also: [Halite's `File::readBytes()` and `File::writeBytes()`](https://github.com/paragonie/halite/blob/ee5e92ee65dfebf26b7d8c559921ce2a5d4cf76c/src/File.php#L973-L1041) API for reference.

This could greatly reduce the amount of `if ($result === false)` lines by making a separate method for stream reading/writing that throws an exception if it can't proceed.
