Replace bare backticks with cli inline markup across all messaging calls

- {.arg} for argument names in stop_/warning_/message_ calls
- {.cls} after "of class" text in format_class() and elsewhere
- {.fun} for function names (replaces `fn()` pattern)
- {.pkg} for tidyverse package names (dplyr, ggplot2)
- {.code} for code literals (TRUE, FALSE, expressions)
- Rewrite print.ab: use cli named-vector with * bullets and code
  highlighting when cli >= 3.0.0; keep plain-text fallback otherwise
- Fix typo in as.sir(): "of must be" -> "or must be"
- switch sir.R verbose notes from message() to message_()

https://claude.ai/code/session_01XHWLohiSTdZvCutwD7ag2b

R/custom_antimicrobials.R

@@ -166,5 +166,5 @@ clear_custom_antimicrobials <- function() {
   n2 <- nrow(AMR_env$AB_lookup)
   AMR_env$custom_ab_codes <- character(0)
   AMR_env$ab_previously_coerced <- AMR_env$ab_previously_coerced[which(AMR_env$ab_previously_coerced$ab %in% AMR_env$AB_lookup$ab), , drop = FALSE]
-  message_("Cleared ", nr2char(n - n2), " custom record", ifelse(n - n2 > 1, "s", ""), " from the internal `antimicrobials` data set.")
+  message_("Cleared ", nr2char(n - n2), " custom record", ifelse(n - n2 > 1, "s", ""), " from the internal {.topic [antimicrobials](AMR::antimicrobials)} data set.")
 }