rust.cmake: fixups
rust.cmake: fixups

- add a default TARGET argument for RustAddLibrary and remove TARGET
  params from the calls--we were already overriding any specified
  TARGET and all the specified TARGETS had bitrot'd
- make CARGO_OPTIONS a CACHE variable so it's scope-independent and
  set the variable to avoid duplicate options (which cargo rejects)

Change-Id: I37eaa421d99834deeb87242aa9acea7e49bed8e3
GitOrigin-RevId: c667372e2961cd052b358abce9602cc888e46daf

AmbiML/sparrow-kata,AmbiML/sparrow-kata,AmbiML/sparrow-kata