feat: scope advisory lock names by scope column values

[zakky21]

Summary

• When scope: option is configured (e.g., scope: :company_id), advisory lock names now include the scope values from the instance
• This prevents unnecessary lock contention across different tenants in multi-tenant environments
• Previously, all operations shared a single lock per model class (ct_{CRC32(class_name)}). Now, scoped models use per-scope locks (e.g., ct_{CRC32(class_name)}_{company_id})

Changes

• Add advisory_lock_name_for(instance) method to SupportAttributes that appends scope values to the base lock name
• Update with_advisory_lock in Support to accept an optional instance argument
• Pass self at all 5 instance-method call sites (_ct_before_destroy, rebuild!, delete_hierarchy_references, add_sibling, find_or_create_by_path)
• Class-method call sites (rebuild!, find_or_create_by_path) pass nil, falling back to model-wide lock

Backward Compatibility

• instance argument defaults to nil — existing callers are unaffected
• Unscoped models return the same lock name as before
• Custom advisory_lock_name option is preserved as the base name

Test plan

• Scoped model (scope: :user_id) generates lock name with scope value suffix
• Different scope values produce different lock names
• Same scope values produce identical lock names
• Multi-scope model (scope: [:user_id, :group_id]) includes all scope values
• Unscoped model returns base lock name unchanged
• nil instance returns base lock name (class-method fallback)
• Full test suite passes (332 tests, 1123 assertions, 0 failures)

Related: #240 (deadlocks during concurrent operations)