BREAK: decouple CSPSolver from particle database

[grayson-helmholz]

• Closes Move particle-database matching out of the CSP solver #340

⚠️ Interface changes

CSPSolver no longer matches its solutions against a particle database. It solves for quantum numbers only, and the matching step moved to the new public function complete_intermediate_states(), which takes a QNResult, its QNProblemSet, and the allowed intermediate states. Re-validating the rules that the solver could not execute moved along with it, since those rules can only run once the intermediate states are complete.

Old name	New name
CSPSolver(allowed_intermediate_states)	CSPSolver(), followed by complete_intermediate_states(result, problem_set, allowed_intermediate_states)

solve() in qrules.workflow performs both steps, so the high-level API is unaffected.

⚙️ Enhancements

• A CSPSolver can now run without a particle database at all. Its solutions carry just the quantum numbers that were solved for, which is what lets later steps work with intermediate states that no particle needs to match.
• _insert_allowed_states() skips intermediate edges for which the solver produced no state instead of raising a KeyError, so partial solutions can be completed.

Squash commit messages

* FEAT: add complete_intermediate_states function