GeezerVison

When no sequence of calls leads to a state that allows the failing
call, the error says so and suggests the constructors that create the
object in such a state, or, if the object can be in several states
depending on the path taken, asks for the same state on every path.
When no call is allowed in the object's state, the error says it is a
final state.

These claims are only made when the state machine models every
state-changing method of the class and of its super and subclasses.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

When nothing is known about the receiver's state, the error lists the
constructors and the calls, with the states they are made from, that
lead to a state allowing the failing call.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

Stacked on #413.

## Description
Building a state machine takes about 25 SMT checks for a small class,
and each check creates its own Z3 context. The machine only depends on
specifications, which are all registered in the first pass, so
`TypeChecker` now builds it on the first state error and reuses it for
every later error in the same checker. Finding the receiver's current
states still runs at each error.

Other options considered:
- **Eagerly, after the first pass, for every class with `@StateSet`:**
correct programs would pay the SMT cost too. Only worth it once
something needs machines without an error, e.g. the fsm diagram.
- **Once per run, cached in `Context`:** `Context` would depend on
`state_machine`, which depends on `context` (a package cycle). The other
way is a static cache that tracks when specifications change. Neither
seemed worth it for the extra hits across classes.

## Cost
Extra time of `TestExamples` on the 269 cases that exist on `main`
(summed per case, one run each; `main` takes 80.3 s):
- #413, without the cache: +29.5 s
- with this PR: +10.6 s, spread over the 54 files with state errors

## Type of change
- [x] Code refactoring

## Checklist
- [x] `mvn test` passes locally

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 5.5 <[email protected]>