Typing for accelerators and plugins

[carmocca]

What does this PR do?

Part of #7035

Before submitting

• Was this discussed/approved via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• [n/a] Did you make sure to update the documentation with your changes? (if necessary)
• [n/a] Did you write any new necessary tests? (not for typos and docs)
• [n/a] Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

PR review

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

[carmocca]

Is this equivalent to what we had before?

[codecov]

Codecov Report

Merging #7022 (e005c44) into master (f645df5) will decrease coverage by 5%.
The diff coverage is 85%.

@@           Coverage Diff           @@
##           master   #7022    +/-   ##
=======================================
- Coverage      92%     87%    -5%     
=======================================
  Files         194     194            
  Lines       12386   12428    +42     
=======================================
- Hits        11414   10774   -640     
- Misses        972    1654   +682