What Changed?

Eagerly visit all IDs in the program under analysis and register potential markers.
Rips out all the infrastructure that was used to do it lazily.

Refactors the CollectingVisitor into two structs, the visitor and then an SPDGGenerator that runs the actual analysis. This separates the concerns out better. The former stores (among other things) a mutable MarkerDatabase that it fills with the markers for local functions and types and it collects a vector of analysis targets.
Once the visit is done it is converted into the SPDGGenerator which stores the read-only MarkerCtx.

Why Does It Need To?

Lazy markers were confusing. Markers on controllers were never registered. Also could cause surprising vacuity if markers were never encountered because e.g. their call sites happened in a closure.

Checklist

• Above description has been filled out so that upon quash merge we have a
  good record of what changed.
• New functions, methods, types are documented. Old documentation is updated
  if necessary
• Documentation in Notion has been updated
  • Remove from list of arguments
  • Remove from step-by-step guide
• Tests for new behaviors are provided
  • New test suites (if any) ave been added to the CI tests (in
    .github/workflows/rust.yml) either as compiler test or integration test.
    Or justification for their omission from CI has been provided in this PR
    description.