Add opt-in lazy computation of the clj-kondo classpath cache

[vemv]

Brief

Fixes nedap/formatting-stack#175

QA plan

• Open a repl having set "-Dformatting-stack.kondo-classpath-cache.runner=delay" beforehand
• Observe that @#'formatting-stack.kondo-classpath-cache/runner-choice evals to clojure.core/delay
• Observe that formatting-stack.kondo-classpath-cache/classpath-cache is a non-derefed Delay object
• deref said object
• note that it takes a while (proving the deferred computation) and then it returns its usual value.

Author checklist

• [x] I have QAed the functionality
• [x] The PR has a reasonably reviewable size and a meaningful commit history
• [x] I have run the branch formatter and observed no new/significative warnings
• [ ] The build passes
• [x] I have self-reviewed the PR prior to assignment
• Additionally, I have code-reviewed iteratively the PR considering the following aspects in isolation:
  • [x] Correctness
  • [x] Robustness (red paths, failure handling etc)
  • [x] Test coverage
  • [x] Spec coverage
  • [x] Documentation
  • intentionally not documented.
  • [x] Security
  • [x] Performance
  • [x] Breaking API changes
  • [x] Cross-compatibility (Clojure/ClojureScript)

Reviewer checklist

• [x] I have checked out this branch and reviewed it locally, running it
• [x] I have QAed the functionality
• [x] I have reviewed the PR
• Additionally, I have code-reviewed iteratively the PR considering the following aspects in isolation:
  • [x] Correctness
  • [x] Robustness (red paths, failure handling etc)
  • [x] Test coverage
  • [ ] Spec coverage
  • [ ] Documentation
  • [ ] Security
  • [x] Performance
  • [x] Breaking API changes
  • [ ] Cross-compatibility (Clojure/ClojureScript)