For breakpoints, allow `NS` (non-susceptible) as a possible outcome of `as.sir()`

[msberends]

Description

We now use substitute_missing_r_breakpoint, but maybe not forcing R but rather NI would make more sense? Not used much in clinics, but perhaps for research?

Recall: CLSI I is not susceptible, while EUCAST I is.

Impacted Field

• Medical (human) microbiology
• Veterinary microbiology
• Environmental microbiology

[msberends]

Now added NS as a possible outcome of as.sir(), but currently without clinical breakpoint interpretation