`mapvotr` alternative to Etalab shapes, using aggregated file

- https://github.com/inseeFrLab/mapvotr
- https://github.com/cedricr/bureau-vote-insee
- https://www.data.gouv.fr/datasets/proposition-de-contours-des-bureaux-de-vote-selon-la-methode-de-linsee

```r
sf::st_read("~/Downloads/contours-bureaux-vote.json") %>%
dplyr::filter(codeCommune== "59350") %>%
dplyr::mutate(numeroBureauVote = codeBureauVote,
codeBureauVote = str_c(codeCommune, numeroBureauVote,
sep = "_")) %>%
readr::write_rds("sorties/contours-Lille-BV.rds")
```

The result is close enough to the Etalab version.

```r
# missing CRS, so add it
ggplot(read_rds("sorties/contours-Lille-BV.rds") %>%
st_set_crs("WGS84")) +
geom_sf(fill = "grey", color = "red", size = 2) +
# saved with CRS 2154
geom_sf(data = read_rds("sorties/contours-Lille-BV-Etalab.rds"),
fill = NA, color = "black", size = 1) +
theme_minimal()

ggsave("insee-v-etalab.png", width = 10, height = 10)
```

# Problem

Won't work with `sfReapportion` straight out of the box, due to missing CRS in `bv_fdc`. If I save `iris_fdc` without reprojecting to 2154 like the code currently does (so, keeping the `RGF93` CRS provided by IGN), I have to pass this to get somewhere, but get an error anyway:

```r
sfReapportion::sfReapportion(st_transform(iris_fdc, "WGS84"),
st_set_crs(bv_fdc, "WGS84"), iris_base,
"CODE_IRIS", "codeBureauVote", "IRIS")
```
```
Error in wk_handle.wk_wkb(wkb, s2_geography_writer(oriented = oriented, :
Loop 0 is not valid: Edge 46 is degenerate (duplicate vertex)
```

This won't work either:

```r
sfReapportion::sfReapportion(st_transform(iris_fdc, 2154),
st_set_crs(bv_fdc, "WGS84") %>%
st_transform(2154), iris_base,
"CODE_IRIS", "codeBureauVote", "IRIS")
```
```
Error during wrapup: scan() expected 'a real', got '7059098.4432252664.'
Error: no more error handlers available (recursive errors?); invoking 'abort' restart
Error during wrapup: TopologyException: side location conflict at 707261.52056810772 7059098.4432252664. This can occur if the input geometry is invalid.
Error: no more error handlers available (recursive errors?); invoking 'abort' restart
```

That same error also comes up when I try the same procedure with `{areal}`, even though the objects pass `areal::ar_validate`:

```r
library(areal)
library(testthat)

# reproject to planar CRS (Lambert 93) and add variables
src <- sf::st_transform(iris_fdc, 2154) %>%
dplyr::left_join(iris_base, by = c("CODE_IRIS" = "IRIS"))
src_vars <- names(iris_base)[ -1 ]
trg <- sf::st_transform(st_set_crs(bv_fdc, "WGS84"), 2154)

stopifnot(areal::ar_validate(src, trg, varList = src_vars))
# areal::ar_validate(src, trg, varList = src_vars, verbose = TRUE)

with_areal <- areal::aw_interpolate(select(trg, -id), tid = "codeBureauVote",
source = src, sid = "CODE_IRIS",
extensive = src_vars,
weight = "total", output = "tibble") %>%
dplyr::select(codeBureauVote, dplyr::all_of(src_vars)) %>%
dplyr::arrange(codeBureauVote) %>%
as.data.frame()

testthat::expect_equal(base_soc, with_areal, tolerance = 1e-4)
```
```
> with_areal <- areal::aw_interpolate(select(trg, -id), tid = "codeBureauVote" .... [TRUNCATED]
Error in `map2()`:
ℹ In index: 1.
ℹ With name: Actifs.
Caused by error in `scan()`:
! scan() expected 'a real', got '7059098.4432252664.'
Run `rlang::last_trace()` to see where the error occurred.
Error in `map2()`:
ℹ In index: 1.
ℹ With name: Actifs.
Caused by error:
! TopologyException: side location conflict at 707261.52056810772 7059098.4432252664. This can occur if the input geometry is invalid.
```

Start by reproducing the sfReapportion and areal examples in the issue, then inspect the CRS and geometry validity of bv_fdc, iris_fdc, and their transformed versions. Compare the resulting errors with the ar_validate output; done means the aggregated bureau shapes work with the shown workflow and the resulting values can be checked against base_soc.

Written by the indexing model from the issue text.