[Bug]: ordering of selected in choices_selected is not respected

### What happened?

Reprex:
```
data <- teal_data()
data <- within(data, {
ADSL <- tmc_ex_adsl
ADSL$EOSDY[1] <- NA_integer_
})
join_keys(data) <- default_cdisc_join_keys[names(data)]

ADSL <- data[["ADSL"]]

app <- init(
data = data,
modules = modules(
tm_t_summary(
label = "Demographic Table",
dataname = "ADSL",
arm_var = choices_selected(c("ARM", "ARMCD"), "ARM"),
add_total = TRUE,
summarize_vars = choices_selected(
variable_choices(ADSL),
c("SEX", "REGION1", "STRATA1")
),
useNA = "ifany"
)
)
)
if (interactive()) {
shinyApp(app$ui, app$server)
}
```

Expected behavior:
- all variables in ADSL as choices in dropdown
- `SEX`, `REGION1`, and `STRATA` selected _in that order_

Actual behavior:
Variables are selected in the order they appear in the dataset

I believe it may be due to this line
https://github.com/insightsengineering/teal.transform/blob/a535ca0c9d674322710b69da826fc48b63b842fd/R/choices_selected.R#L174-L177

Perhaps this is not a bug and just your desired behavior, but it seems to me that the ordering of the `selected` argument should be respected in the UI upon launch. Currently, to get around this, I can specify the `subset` argument in `variable_choices`. However, if I wish to have all ADSL variables, specifying _all_ of them in some preferred order seems like it should not be necessary.

### sessionInfo()

```R
R version 4.2.1 (2022-06-23)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: CentOS Linux 7 (Core)

Matrix products: default
BLAS/LAPACK: /fsx-perm/SERVICES/WISE/easybuild/software/OpenBLAS/0.3.12-GCC-10.2.0/lib/libopenblas_skylakexp-r0.3.12.so

locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
[3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats graphics grDevices datasets utils methods
[7] base

other attached packages:
[1] teal.modules.clinical_0.10.0 tern_0.9.7
[3] rtables_0.6.12 magrittr_2.0.3
[5] formatters_0.5.11 teal.transform_0.6.0
[7] teal_0.16.0 teal.slice_0.6.0
[9] teal.data_0.7.0 teal.code_0.6.1
[11] shiny_1.10.0

loaded via a namespace (and not attached):
[1] nlme_3.1-164 geeasy_0.1.2
[3] teal.logger_0.3.2 fontawesome_0.5.3
[5] RColorBrewer_1.1-3 numDeriv_2016.8-1.1
[7] tools_4.2.1 TMB_1.9.17
[9] backports_1.5.0 bslib_0.9.0
[11] R6_2.6.1 DT_0.33
[13] mgcv_1.9-1 MESS_0.5.12
[15] withr_3.0.2 tidyselect_1.2.1
[17] shinyvalidate_0.1.3 emmeans_1.11.1
[19] compiler_4.2.1 cli_3.6.5
[21] formatR_1.14 shinyjs_2.1.0
[23] sandwich_3.1-1 sass_0.4.9
[25] mosaicCore_0.9.4.0 scales_1.4.0
[27] checkmate_2.3.2 mvtnorm_1.3-3
[29] ggridges_0.5.6 stringr_1.5.1
[31] digest_0.6.37 ggformula_0.12.0
[33] minqa_1.2.8 rmarkdown_2.29
[35] pkgconfig_2.0.3 htmltools_0.5.8.1
[37] lme4_1.1-37 teal.widgets_0.4.3
[39] geeM_0.10.1 labelled_2.14.0
[41] fastmap_1.2.0 htmlwidgets_1.6.4
[43] rlang_1.1.6 rstudioapi_0.17.1
[45] jquerylib_0.1.4 farver_2.1.2
[47] generics_0.1.4 zoo_1.8-13
[49] jsonlite_1.9.1 dplyr_1.1.4
[51] Matrix_1.6-0 Rcpp_1.0.14
[53] shinycssloaders_1.1.0 clipr_0.8.0
[55] geepack_1.3.12 logger_0.4.0
[57] lifecycle_1.0.4 stringi_1.8.7
[59] multcomp_1.4-28 yaml_2.3.10
[61] MASS_7.3-60.0.1 grid_4.2.1
[63] tern.gee_0.1.5 promises_1.3.2
[65] forcats_1.0.0 lattice_0.22-6
[67] haven_2.5.4 splines_4.2.1
[69] nestcolor_0.1.3 hms_1.1.3
[71] knitr_1.50 pillar_1.10.2
[73] boot_1.3-30 estimability_1.5.1
[75] codetools_0.2-20 glue_1.8.0
[77] evaluate_1.0.3 renv_1.1.4
[79] vctrs_0.6.5 nloptr_2.2.1
[81] httpuv_1.6.15 Rdpack_2.6.4
[83] gtable_0.3.6 purrr_1.0.4
[85] tidyr_1.3.1 cachem_1.1.0
[87] ggplot2_3.5.2 xfun_0.51
[89] mime_0.13 rbibutils_2.3
[91] xtable_1.8-4 broom_1.0.8
[93] teal.reporter_0.4.0 later_1.4.1
[95] reformulas_0.4.1 rsconnect_1.3.4
[97] survival_3.6-4 tibble_3.3.0
[99] glmmTMB_1.1.10 memoise_2.0.1
[101] shinyWidgets_0.9.0 TH.data_1.1-3
```

### Relevant log output

```R

```

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