GeezerVison

Stacked on #411.

## Description
When no call can fix a failing state transition, the error now says why:
- **Unreachable state:** no sequence of calls reaches a state where the
call is allowed. The hint suggests a constructor that creates the object
in such a state, if one exists.
- **State depending on the path taken:** the object can be in several
states (e.g. after an `if`), and no single sequence of calls works for
all of them.
- **Final state:** no method with a state refinement can be called in
any of the states the object can be in.

These hints claim that something is impossible, so they are only given
when the machine is complete. That means every state-changing method of
the class is modeled, and no superclass or subclass has state
refinements of its own. When nothing is known about the state, these
hints are not given; the next PR handles that case.

`StateMachineBuilder` now also records the states each constructor
creates, when they only depend on the state of `this`.

## Example
```java
f.close();
f.read(); // read() needs open
```
```
 --> No sequence of calls moves f from closed to open. Create a new object instead with new File()
     f is in state closed, where none of its methods with state refinements can be called
```

## Type of change
- [x] New feature

## Checklist
- [x] Added tests:
  - `ErrorStateHintFinalState` and `ErrorStateHintPathDependent`.
- `ErrorStateHintIncomplete` (a transition depends on an argument) and
`ErrorStateHintSubclass` (a subclass adds a transition) get no dead-end
claim.
  - `ErrorStateHintSeveralRefinements` now gets the path-dependent hint.
- [x] `mvn test` passes locally

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

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

## Description
#412, #413 and #414 were merged into their stacked base branches instead
of `main`: once #411 was merged, their bases were never retargeted.
Their code is only on `feat/state-hints-unknown`.

This PR applies the three reviewed commits on top of `main`, unchanged:
- Explain dead ends in failing state transitions (#412)
- List the calls that reach an allowed state when the state is unknown
(#413)
- Build each class's state machine once per checker (#414)

The hint and state machine files are identical to
`feat/state-hints-unknown`. Rebase-merging keeps the three commits
separate.

## Checklist
- [x] `mvn test` passes locally on top of the current `main` (#408,
#409)

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

---------

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