* [Build] Add precompiled headers for Qt-backed executables
Reparsing QtCore/QtGui/QtWidgets/QtNetwork in ~460 client translation
units is the dominant compilation cost. Precompile the two common layers:
- qtcore_pch.h (Qt Core only; safe even for headless Servatrice)
- qtwidgets_pch.h (adds Gui/Widgets/Network; used by Cockatrice and Oracle)
target_precompile_headers() requires CMake 3.16, now the project minimum.
Estimated 30-50% faster client rebuilds.
* [Build] Format qtwidgets precompiled header
clang-format include regrouping and a missing trailing newline.
* [Build] Add PCH-aware ccache sloppiness config; format cmake/pch headers
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Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
