Disable learnr exercise checker in R Markdown templates

[Copilot]

knitr interprets chunk labels ending in -check as learnr exercise check chunks, requiring tutorial_options() configuration. This caused vignette builds to fail with: An exercise check chunk exists ('exonorm-check') but an exercise checker function is not configured.

Changes

• Report templates: Added options(tutorial.exercise.checker = NULL) to setup chunks in inst/rmarkdown/index.Rmd and inst/rmarkdown/module.Rmd
• Vignettes: Added setup chunks with the same option to vignettes/report.Rmd, vignettes/usage.Rmd, and vignettes/spatial.Rmd

```{r setup, include=FALSE}
# Disable tutorial exercise checking to prevent chunks ending in
# '-check' from being interpreted as learnr exercise check chunks
options(tutorial.exercise.checker = NULL)
knitr::opts_chunk$set(echo = TRUE)

This prevents knitr from activating learnr hooks for dynamically generated reports and vignettes.

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<details>

<summary>Original prompt</summary>

> Error in hook(params) : 
>   An exercise check chunk exists ('exonorm-check') but an exercise checker function is not configured for this tutorial. Please use `tutorial_options()` to define an `exercise.checker`.
> Calls: <Anonymous> ... process_group -> call_block -> as.strict_list -> hook
> 
> Quitting from 25_rnaseq.Rmd:979-984 [exonorm-check]
> Execution halted


</details>



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