OptionaldirectoryName of the OPFS sub-directory holding the temporary files.
OptionalgetReturns (or resolves to) the root FileSystemDirectoryHandle. Defaults to navigator.storage.getDirectory().
Provide it to run inside a worker with a pre-obtained handle, or to test against a mock.
OptionalthresholdSpill a buffered entry to a file once its buffered data exceeds this size, in bytes. Smaller entries stay in memory.
Options for createOPFSTempStream.