List of changes:
1. Optimizations in FileTransfer. a. Use `stream.forEach` instead of `await for`. b. Type cast `List<int>` to `Uint8List` instead of using `Uint8List.fromList` results in (presumably) fewer copy and faster execution. c. Iterate through `Uint8List` with regular for loop instead of for-in loop.
2. Precache the block hashes of a file, and reuse it on subsequent runs.
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