Prevent UnicodeDecodeError when relaying child stdout – decode with errors="replace"

[jistiak]

flet_cli/commands/run.py crashed whenever the spawned process wrote non-UTF-8 bytes to stdout (e.g. OpenCV, C printf, binary progress bars).

What & Why:
Running flet run on long-lived apps that spawn helper processes (e.g. camera capture, FFmpeg, OpenCV) eventually blows up with

UnicodeDecodeError: 'utf-8' codec can't decode byte 0x91 in position …

because print_output() assumes p.stdout.readline() always returns valid UTF-8. Native libraries often write raw bytes directly to FD 1, bypassing Python’s I/O wrappers, so invalid sequences slip through and crash the thread.

Fix
line = p.stdout.readline().decode("utf-8", errors="replace")

errors="replace" converts any bad byte to �, guaranteeing the read never raises.

Behaviour is unchanged for valid UTF-8; the only difference is that the CLI now lives instead of dying.

Summary by Sourcery

Bug Fixes:

• Decode stdout lines with errors="replace" to avoid crashes on non-UTF-8 bytes

[sourcery-ai]

We've reviewed this pull request using the Sourcery rules engine

[CLAassistant]

All committers have signed the CLA.

[FeodorFitsner]

Is this PR superseded by #5397?