Fix download progress bar stuck at 0% (adb pull is silent when piped)

[kapshytar]

Problem

When downloading a file (external adb mode), the progress popup stays at "Waiting... 0%" for the entire transfer and only jumps to done at the very end.

Root cause

UpDownHelper.call parses adb's [ N%] progress lines — but adb pull only prints that progress to a TTY. When its stdout is piped (as CommonProcess does), adb stays completely silent until the transfer finishes and just prints the final … 1 file pulled … X MB/s summary. So the percentage parser never receives anything and the bar never moves.

You can confirm it:

$ adb pull /sdcard/big.bin /tmp/ | cat
/sdcard/big.bin: 1 file pulled, 0 skipped. 21.4 MB/s (...)   # no % lines at all

Fix

In android_adb.FileRepository.download, derive progress from the local side instead of relying on adb's (absent) output:

1. Query the remote file size once up front via stat (space-safe through shlex.join).
2. While adb pull runs, poll the size of the file being written locally on a background thread and emit progress_callback(name, percent).

This mirrors the fallback the Flutter client (FileDroid) already uses for the same adb limitation.

Testing

Pulling a 60 MB file now reports streaming progress:

[5, 13, 21, 28, 36, 45, 53, 61, 70, 80, 88, 98, 100]

instead of nothing. No change to the python-adb (adb-shell) path, which already reports progress.