feat: revenue_concept = c("general", "total") off the crosswalk (#12)

Closes the last blocked test in the suite. Owner ruled both halves of the
open question yes on 2026-07-30.

`cog_revenue()` gains `revenue_concept`, mirroring `expenditure_concept`,
with Census's two published concepts defined as crosswalk
`revenue_subtype` sets rather than item-code prefixes:

  general = own_source + federal + state + local_aid   (the default)
  total   = general + utility + liquor_store + insurance_trust

The manual defines the first by subtracting the other three from the
second (4.3), so both are computable only once all four families are
named -- which cog_pipeline#79 does. Insurance trust now includes the
employee-retirement X codes (X01/X02/X05/X08) alongside the Y codes.

- inst/sql: revenue_long / revenue_long_harmonized carry EVERY revenue
  subtype; the concept narrows in R via the existing subtype_scope
  machinery, exactly as expenditure_concept narrows spending_long.
- cog_explain() now prints each verb's OWN concept. It previously
  printed `expenditure_concept` unconditionally, so a cog_revenue()
  caller was told "Concept: primary" -- a spending concept their result
  has nothing to do with.
- Fixture regenerated at pipeline_commit aadb46b (330 crosswalk rows).

Corrected two stale expectations in the blocked test while un-skipping
it. It asserted X01+X04+X05+X08 and omitted X02, which applies to state
governments and is nonzero for Wisconsin; X04 is an exhibit code for an
INTRAgovernmental transfer that Census's own "Total Emp Ret Rev"
excludes. Verified against that Census field: the right set is
X01+X02+X05+X08 = $2,283,883k, exactly. And its expected `total` of
$33,377,093k predated the Y codes being classified -- complete Total
Revenue for WI FY2012 is $34,881,961k (general 31,338,293 + Y 1,259,785
+ X 2,283,883).

Behaviour change worth knowing: `general` is now STRICT Census General
Revenue, so utility and liquor store revenue leave the default. Measured
on the fixture that is 15.9% of what cog_revenue() returned for cities,
vs 1.2% for states and 1.7% for counties.

Suite: 716 pass / 0 fail / 0 skip -- the first time this package has had
no skipped tests.

Closes #12

tests/testthat/test-categories.R

@@ -49,12 +49,14 @@ test_that("cog_categories(type = 'revenue') returns only revenue rows", {
   skip_if_no_corpus()
   r <- cog_categories(type = "revenue")
   expect_true(all(r$category_type == "revenue"))
-  # `insurance_trust` (Y01/Y02/Y04/Y11/Y12/Y51/Y52) is deliberately NOT
-  # own_source: Census's "General Revenue" excludes insurance trust revenue,
-  # and Y01 alone is $1.31T corpus-wide.
+  # The four non-general subtypes are deliberately NOT own_source: Census's
+  # General Revenue excludes insurance trust (Y01 alone is $1.31T corpus-wide,
+  # plus the employee-retirement X codes), utility (A91-A94) and liquor store
+  # (A90) revenue by definition, which is what makes both of its published
+  # revenue concepts computable -- see `revenue_concept` in `?cog_revenue`.
   expect_true(all(r$subtype %in%
                   c("own_source", "federal", "state", "local_aid",
-                    "insurance_trust")))
+                    "insurance_trust", "utility", "liquor_store")))
 })
 
 test_that("cog_categories(pattern = ...) filters case-insensitively", {