to_lower() in check_names() causes error if upper cases used.

[dhope]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce

library(ARUtools)
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union

library(purrr)
#> 
#> Attaching package: 'purrr'
#> The following object is masked from 'package:base':
#> 
#>     %||%

library(tidyr)
library(glue)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union

s <- clean_site_index(example_sites_clean,
                      name_date = c("date_time_start", "date_time_end")
)
m <- clean_metadata(project_files = example_files) |>
  add_sites(s) |>
  calc_sun() |>
  mutate(
    time_period = if_else(hour(date_time) < 6, "early", "late"),
    year = year(date)
  )
#> Extracting ARU info...
#> Extracting Dates and Times...
#> Joining by columns `date_time_start` and `date_time_end`

p <- list(
  "early" = sim_selection_weights(min_range = c(-70, 240)),
  "late" = sim_selection_weights(min_range = c(100, 300), min_mean = 200)
)

w <- m |>
  nest(data = c(-time_period, -year)) |>
  mutate(
    params = p,
    sel = map2(data, params, calc_selection_weights)
  ) |>
  unnest(sel) |>
  select(-"data", -"params") |>
  mutate(Selection_group = glue("{site_id}_{year}_{time_period}"))
n <- w |>
  summarize(n_recordings = n(), .by = c("Selection_group", "time_period")) |>
  mutate(
    n = if_else(time_period == "early", 5, 2),
    n_os = if_else(time_period == "early", floor(n * 1 / 3), floor(n * 1 / 4)),
    n_os = pmax(0, pmin(n_recordings - n, round(n / 3))),
    n = pmin(n, n_recordings)
  )

g <- sample_recordings(w, n,
                       col_site_id = Selection_group,
                       col_sel_weights = psel_normalized
)
#> Error in `sample_recordings()`:
#> ! Problems with data `n`:
#> • Column 'Selection_group' does not exist

^{Created on 2024-07-03 with reprex v2.1.0.9000}

Expected behavior
Having upper case column names shouldn't cause the function to fail and if that is wanted, it should at least be clear about why it is throwing an error.

[dhope]

Fixed for now with 57ac7a7, however still have some concerns about use of tolower() in check_names()