Slow start speed

[khlopko]

Improve startup times of the build server by caching options results instead of querying each time.

[khlopko]

Can buildTarget/prepare be used to start work?

Pipe xcodebuild calls straight to cache files.

[khlopko]

a4e720e introduces caching of build settings

[khlopko]

current bottleneck is xcodebuild necessity to obtain indexing data for LSP; potential fix connecting to xcode build service via xpc to obtain metadata faster (or maybe swift-build system based on that can be a shortcut).