CI: use modern cmake features, -Werror and parallel testing

[mwtoews]

This is yet another CI refresh, but mostly to improve some cmake(1) features:

• Use -Werror=dev (cmake<4.4) or -Werror=author (cmake>=4.4) for CMake configure to raise errors on warnings from CMake intended for the authors (us) to see
• Try to use the cmake -S <src-dir> -B <build-dir> configure pattern rather than the mkdir build && cd build && cmake .. pattern
• Use cmake --build <build-dir> rather than make or ninja; cmake --install <build-dir> rather than make install
• Use the CMAKE_BUILD_PARALLEL_LEVEL env var to control the number of processors for building
• Use the CTEST_PARALLEL_LEVEL env var to allow parallel testing

Miscellaneous changes with ci/fedora_rawhide/start.sh:

• Add some test dependencies
• A few cache-related fixes

Miscellaneous changes with ci/install.sh:

• Raise an error if $TRAVIS is defined (not supported anymore), since there was special logic needed to support this
• Disable test adding non-official file to DB, since transformations_czechia_extra.sql no longer exists; add TODO to potentially re-enable
• Remove test setting CMAKE_INSTALL_INCLUDEDIR/CMAKE_INSTALL_LIBDIR/CMAKE_INSTALL_BINDIR to absolute directories, since this is discouraged (was there a use case for this?)