cleaning BiocCheck(); linting revision; GHA bump to Bioc devel

[HelenaLC]

BiocCheck-related changes

• dropped LazyData: in the DESCRIPTION as advised by Bioc; example data is now loaded explicitly on demand
• implemented Bioc code guidelines as outlined here, e.g.:
  • fixed indentation and consistent spacing (e.g., after , and logical operators, not after = etc.)
  • fixed SCE data handling with corresponding accessors (instead of @)
  • keeping to an 80-character line limit when sensible

other updates

• rewrote code to rid of various deprecated functions (e.g., magrittr::not, purrr::when)
• various code simplifications, e.g., use of base R instead of tidy-syntax when sensible
• removed unused image files and move plotly example PNG to inst/extdata
• updated GHA to use Bioconductor devel