Minimize dependencies from `Anneal.lean`, generated Lean

[joshlf]

Currently, we depend on all of Aeneas in Anneal.lean, leading to multi-second import times from lake build. Instead, we should:

• Minimize these imports
• Refactor Anneal.lean so that it contains distinct modules which only depend narrowly on the parts of Aeneas which they need
• Provide this library as an external dependency (perhaps installed via cargo anneal setup?) and, in generated Lean, only import the needed modules (and allow users to import more for their own annotations)