Allow external adjustment of parallel search workers #204

Job	Run time
build-32-bit-linkage	43s
build-autoconf (ubuntu-latest)	4m 42s
build-cmake-qt-gist	6m 6s
build-cmake-windows-vcpkg	41m 36s
build-cmake-unix-ninja	14m 9s
tidy	10s
build-cmake-unix (ubuntu-latest, ON)	20m 26s
build-cmake-unix (macos-15, OFF)	10m 0s
build-autoconf-windows	16m 38s
build-cmake-qt5-gist-smoke	5m 20s
build-cmake-windows-msys2	8m 59s
build-autoconf (macos-15)	4m 27s
build-cmake-windows (shared, ON, OFF)	23m 52s
build-cmake-windows (static, OFF, ON)	18m 22s
	2h 55m 30s

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