Reduce cyclomatic complexity of expressions/routines over 25

[MichaelChirico]

25 seems like a reasonable target for simplifying implementations/delegating to helper functions. Here are the functions/expression that are flagged as having a higher complexity currently:

R/bit.R:223:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 55 to at most 25.
bitwhich <- function(
^
R/bit.R:2446:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 29 to at most 25.
`[<-.bit` <- function(x, i, value) {
^
R/bit.R:2710:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 43 to at most 25.
`[<-.bitwhich` <- function(x, i, value) {
^
tests/testthat/test-bit.R:510:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 43 to at most 25.
test_that("aggregation functions work", {
^
tests/testthat/test-old-regtest.R:2:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 99 to at most 25.
regtest.bit <- function(N = 50) {
^
vignettes/bit-performance.Rmd:371:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 47 to at most 25.
for (n in names(binaryDomain)) {
^