BREAK: map conservation rules to priorities

[grayson-helmholz]

• Closes Merge conservation_rules and rule_priorities attributes #279

⚠️ Interface changes

EdgeSettings and NodeSettings now carry the rules and their priorities in a single field. conservation_rules became a mapping of each rule to its priority (rules with a higher priority are evaluated first), so the separate rule_priorities field disappears. A set is still accepted as input: a converter normalizes it to a mapping in which every rule gets the new DEFAULT_RULE_PRIORITY (1), but reading the attribute back always yields a dict.

Old name	New name
EdgeSettings.rule_priorities	removed, folded into EdgeSettings.conservation_rules
NodeSettings.rule_priorities	removed, folded into NodeSettings.conservation_rules
EdgeSettings.conservation_rules: set[GraphElementRule]	EdgeSettings.conservation_rules: dict[GraphElementRule, int]
NodeSettings.conservation_rules: set[Rule]	NodeSettings.conservation_rules: dict[Rule, int]

Priorities are now attached per rule instance rather than looked up by rule type, which simplifies filter_quantum_number_problem_set() and _get_rules_by_priority(). create_interaction_settings() still derives its mappings from EDGE_RULE_PRIORITIES and CONSERVATION_LAW_PRIORITIES, so the default interaction settings are unchanged.

❗ Behavioral changes

• In the DOT output of qrules.io, a rule without a declared priority is now rendered with its effective priority 1 instead of NA, and the RULES block is emitted whenever a setting has any rules, not only when priorities were declared separately.

Squash commit messages

* BEHAVIOR: render unprioritized rules with priority 1