mdro(): infer base drug resistance from drug+inhibitor combination columns (#209)

When a base beta-lactam column (e.g., piperacillin/PIP) is absent but a
corresponding drug+inhibitor combination (e.g., piperacillin/tazobactam/TZP)
is present and resistant, resistance in the base drug is now correctly
inferred. This is clinically sound: resistance in a combination implies the
inhibitor provided no benefit, so the base drug is also resistant.

Susceptibility in a combination is NOT propagated to the base drug (the
inhibitor may be responsible for susceptibility), so only R values are
inferred; missing base drugs remain NA otherwise.

Implementation details:
- Uses AB_BETALACTAMS_WITH_INHIBITOR to identify all beta-lactam+inhibitor
  combinations present in the user's data
- Derives base drug AB codes by stripping the "/inhibitor" part from names
- Creates synthetic proxy columns (.sir_proxy_<AB>) in x, set to "R" when
  any matching combination is R, otherwise NA
- Proxy columns are added to cols_ab before drug variable assignment,
  so all existing guideline logic benefits without any changes
- Multiple combos for the same base drug are OR-ed (any R → R)
- Adds internal ab_without_inhibitor() helper for the name->base mapping
- Verbose mode reports which combinations are used for inference

Bumps version: 3.0.1.9028 -> 3.0.1.9029

https://claude.ai/code/session_01Cp154UtssHg84bw38xiiTG

NEWS.md

@@ -1,4 +1,4 @@
-# AMR 3.0.1.9028
+# AMR 3.0.1.9029
 
 ### New
 * Integration with the **tidymodels** framework to allow seamless use of SIR, MIC and disk data in modelling pipelines via `recipes`
@@ -18,6 +18,7 @@
 * Two new `NA` objects, `NA_ab_` and `NA_mo_`, analogous to base R's `NA_character_` and `NA_integer_`, for use in pipelines that require typed missing values
 
 ### Fixes
+* `mdro()`: when a base beta-lactam drug column is missing but a corresponding drug+inhibitor combination is present in the data and resistant (e.g., piperacillin/tazobactam = R while piperacillin is absent), the base drug is now correctly inferred as resistant. This ensures MDRO classification is not missed due to test-ordering differences in the laboratory. The reverse direction is also valid: susceptibility in a combination does not imply susceptibility in the base drug (the inhibitor may be responsible), so only resistance is propagated. Closes #209
 * Fixed a bug in `as.ab()` where certain AB codes containing "PH" or "TH" (such as `ETH`, `MTH`, `PHE`, `PHN`, `STH`, `THA`, `THI1`) would incorrectly return `NA` when combined in a vector with any untranslatable value (#245)
 * Fixed a bug in `antibiogram()` for when no antimicrobials are set
 * Fixed a bug in `as.sir()` where for numeric input the arguments `S`,  `I`,  and `R` would not be considered (#244)