perf(core): optimize nest_for_ard group partitioning, process_nested_list, and batch apply_fmt_fun

[kpagacz]

Flamegraph profiling of cards::ard_summary() and cards::ard_missing() revealed following possible performance gains:

1. cards::nest_for_ard() dynamically generated quosures and executed dplyr::filter() and dplyr::select() G times across all N observations (O(G * N) complexity), repeatedly scanning the dataset and evaluating tidyselect column specifications.
2. .process_nested_list_as_df() executed per-variable dplyr::filter() followed by dplyr::rows_update(), forcing hash key table validation and full dataframe copies.
3. cards::apply_fmt_fun() performed row-by-row purrr::pmap() iteration, resolving function aliases, creating closures via label_round(), and executing scalar format() calls independently for each cell (!!).

Changes:

1. cards/R/nest_for_ard.R:

   • Replaced dynamic quosure filtering loop with O(N) integer index matching via vctrs::vec_match() against the unique group combination grid.
   • Sliced row subsets directly using base R matrix/dataframe indexing on pre-split integer indices, refactoring out dplyr::filter() and tidyselect evaluations per stratum.
   • Replaced mutate(across(..., as.list)) with direct in-place list column wrapping.

2. cards/R/ard_summary.R:

   • Refactored .process_nested_list_as_df():
     • Extracted unique (variable, stat_name) pairs upfront and grouped into a lookup list.
     • Calculated formula selectors per variable and computed 1-to-1 integer indices via vctrs::vec_match().
     • Replaced dplyr::rows_update() with direct positional assignment x[[new_column]][idx] <- vals.

3. cards/R/apply_fmt_fun.R:

   • Grouped rows sharing identical fmt_fun definitions and resolved function aliases once per group rather than per row.
   • Vectorized formatting across statistic vectors for supported primitive and standard rounding functions, falling back to scalar evaluations only when required.
   • Maintained full condition capture parity (stat_fmt, warning, error) matching existing ARD S3 structure.

What changes are proposed in this pull request?

• optimize nest_for_ard group partitioning, process_nested_list, and batch apply_fmt_fun, @kpagacz

Reference GitHub issue associated with pull request. e.g., 'closes #'

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Optional Reverse Dependency Checks:

Install checked with pak::pak("Genentech/checked") or pak::pak("checked")

# Check dev versions of `cardx`, `gtsummary`, and `tfrmt` which are in the `ddsjoberg` R Universe
Rscript -e "options(checked.check_envvars = c(NOT_CRAN = TRUE)); checked::check_rev_deps(path = '.', n = parallel::detectCores() - 2L, repos = c('https://ddsjoberg.r-universe.dev', 'https://cloud.r-project.org'))"

# Check CRAN reverse dependencies but run tests skipped on CRAN
Rscript -e "options(checked.check_envvars = c(NOT_CRAN = TRUE)); checked::check_rev_deps(path = '.', n = parallel::detectCores() - 2, repos = 'https://cloud.r-project.org')"

# Check CRAN reverse dependencies in a CRAN-like environment
Rscript -e "options(checked.check_envvars = c(NOT_CRAN = FALSE), checked.check_build_args = '--as-cran'); checked::check_rev_deps(path = '.', n = parallel::detectCores() - 2, repos = 'https://cloud.r-project.org')"