feat: cog_find_peers + cog_peer_compare

cog_find_peers selects peers from canonical_fips_xwalk by same-type,
same-state, and population-range (ratio or absolute) criteria,
ordered by |log(pop_ratio)| ascending.

cog_peer_compare accepts the find_peers result (or a plain character
vector of govids), pulls spending for target + peers via cog_spending,
and appends summary rows (summary_p25/p50/p75) so the whole result
can be faceted by `role` in a single ggplot call. Summary rows honor
per_capita + adjust_to_year by picking the right value column.
target_rank reports the target's rank among target+peers at max(years).

Provenance is rewritten with verb = cog_peer_compare and peer_count.

Also: globalVariables('.data') in zzz.R to silence R CMD check on
tidy-eval pronouns.

Tests: 21 new / 120 total pass. devtools::check() 0E/0W/2N.

man/cog_find_peers.Rd

@@ -0,0 +1,45 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/peers.R
+\name{cog_find_peers}
+\alias{cog_find_peers}
+\title{Find peer governments by similarity criteria}
+\usage{
+cog_find_peers(
+  target_govid,
+  same_type = TRUE,
+  same_state = FALSE,
+  pop_range = c(0.7, 1.3),
+  is_ratio = TRUE,
+  pop_year = NULL,
+  max_peers = 10L
+)
+}
+\arguments{
+\item{target_govid}{Character scalar — `canonical_govid` of the target.}
+
+\item{same_type}{If `TRUE` (default) restrict peers to the target's
+`govs_type`.}
+
+\item{same_state}{If `TRUE` restrict peers to the target's `fips_state`.
+Default `FALSE`.}
+
+\item{pop_range}{Length-2 numeric vector giving lower/upper bounds.}
+
+\item{is_ratio}{If `TRUE` (default) `pop_range` is multiplied by the
+target's `population_acs` to produce absolute bounds. If `FALSE`,
+`pop_range` is interpreted as absolute population counts.}
+
+\item{pop_year}{Reserved for future use (selecting ACS vintage). Currently
+the corpus has a single snapshot so this argument has no effect.}
+
+\item{max_peers}{Integer cap on the number of peers returned.}
+}
+\value{
+Tibble with columns `canonical_govid`, `gov_name`, `fips_state`,
+  `population_acs`, `pop_ratio`, `rank`.
+}
+\description{
+Selects peer governments from `canonical_fips_xwalk` by combinations of
+government type, state, and population range. Peers are ordered by
+`|log(pop_ratio)|` ascending (closest to the target's population first).
+}