feat(explain): render new per-capita provenance fields

cog_explain() now prints denominator_source, popyear_range, and
pop_source_counts under the Transformations section.

R/explain.R

@@ -74,6 +74,16 @@ cog_explain <- function(result, format = c("print", "list")) {
   pc <- prov$transformations$per_capita
   if (isTRUE(pc$applied)) {
     cli::cli_text("Per-capita denominator: {pc$denominator_source}")
+    if (length(pc$popyear_range) == 2L) {
+      cli::cli_text(
+        "  popyear range: {pc$popyear_range[1]}-{pc$popyear_range[2]}"
+      )
+    }
+    if (!is.null(pc$pop_source_counts)) {
+      cli::cli_text(
+        "  pop_source counts: census_f33={pc$pop_source_counts$census_f33}, unavailable={pc$pop_source_counts$unavailable}"
+      )
+    }
   }
   infl <- prov$transformations$inflation
   if (isTRUE(infl$applied)) {

tests/testthat/test-explain.R

@@ -30,3 +30,18 @@ test_that("cog_explain errors on non-verb input", {
   df <- tibble::tibble(a = 1)
   expect_error(cog_explain(df), "provenance")
 })
+
+test_that("cog_explain prints denominator + popyear_range + counts", {
+  skip_if_no_corpus()
+  with_fixture_corpus({
+    r <- cog_spending("101006006", years = 2019:2020,
+                      category = "Police", per_capita = TRUE)
+    out <- paste(c(
+      capture.output(cog_explain(r)),
+      capture.output(cog_explain(r), type = "message")
+    ), collapse = "\n")
+    expect_true(grepl("Census F-33", out))
+    expect_true(grepl("popyear", out, ignore.case = TRUE))
+    expect_true(grepl("census_f33", out))
+  })
+})