By setting the deprecation version for KRunner to 5.91,
the negated deprecation wrapper will evaulate to true and
we get compatibility typedefs.
This way we do not need to add the typedefs manually or
add `using namespace Plasma` to the plugins.
Task: https://phabricator.kde.org/T15140
If libqalculate is not present on the system, calculator runner falls
back to using QJSEngine, which results in significantly reduced
precision. Make calculator runner unconditionally dependent on
Qalculate and remove conditional fallback code to QJSEngine.
BUG: 433730