Derive norm count subtype internally

[phoman14]

Changes

• Derive sub_count_type = "voom" internally when count_type is norm.
• Stop exposing the default sub_count_type parameter in the Code Ocean app panel or CLI.
• Add tests that run main.R with raw, filt, norm, and batch count types.

Issues

No linked issues.

PR Checklist

(Strikethrough any points that are not applicable.)

• This comment contains a description of changes with justifications, with any relevant issues linked.
• Run the capsule in Code Ocean and ensure it completes successfully with no errors.
• Update CHANGELOG.md with a short description of any user-facing changes and reference the PR number. Follow the style described in https://style.tidyverse.org/news.html
• The tests workflow succeeds on the latest commit.