[Feature Request]: Remove `yaml_utils.R`

[averissimo]

Feature description

These functions are potentially not necessary and can be replaced with yaml::as.yaml(x, handlers = list(...)) for custom printing.

Benefit:

• Less code to maintain
• Standard teal.reporter.rmd_yaml_args that is closer to the actual yaml options
  • toc is not a first level option

# New option format
list(
  author = "NEST",
  title = "Report",
  date = as.character(Sys.Date()),
  output = list(html_document = list(toc = FALSE))
) |> yaml::as.yaml() |> cat()
#> author: NEST
#> title: Report
#> date: '2025-09-02'
#> output:
#>   html_document:
#>     toc: no

Cons:

• Function is exported, so it needs to be deprecated
• Added logic to support former logic (toc as first-level option and as dependency of output)

#391 draft PR supports this.

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