Testing sync and bypassCache for WriteStream and ReadStream

[0xnullifier]

Testing sync and bypass.Cache flags for 'WriteStream' and 'ReadStream' should validate these critical behaviors:

Confirm WriteStream with sync=true ensures that data is instantly stored to disk (use direct disk reads to test), whereas sync=false may postpone the writing by some mechanism say simulating a heavy filesystem task in a go routine.

Second, ensure that ReadStream with bypassCache=true always reads from disk, even if data is cached (check by updating the underlying file and validating ReadStream provides the updated data), whereas bypassCache=false should return cached data if available.