feat: `flet test` on-device integration testing + CI matrix (#6623) #2777

Job	Run time
Build Flet Flutter package	45s
Build Documentation	45s
Python 3.11 tests	22s
Python 3.10 tests	24s
Python 3.14 tests	24s
Python 3.12 tests	31s
Python 3.13 tests	25s
Build Flet extensions	1s
Build Flet Client for Linux ${{ matrix.title }}	1s
Build Flet Client for Windows	1s
Build Flet Client for Web	1s
Build flet, flet-cli and flet-desktop Python packages	1s
Package templates	1s
Build Flet Client for macOS	1s
Publish GitHub Release	1s
Publish Python packages to PyPI	1s
	3m 45s

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