Refactor remaining internal ignored state to transient terminology

[taljeon]

Summary

• complete the remaining internal terminology work after Issue 1825 - Refactor internal references to ignored (attributes) to transient attributes #1828 renamed the attribute-list filtering APIs
• rename the internal transient-attribute flag and readers from ignored to transient
• update declaration, attribute-list, and definition-proxy internals without changing public behavior
• add unit coverage for persistent and transient attribute state

Closes #1825

Testing

• focused RSpec: 58 examples, 0 failures
• unit RSpec: 334 examples, 0 failures
• acceptance RSpec: 441 examples, 0 failures
• Cucumber: 4 scenarios, 18 steps, all passed
• Standard on all 10 changed files: no offenses

Repository-wide Standard under Ruby 4 also reports three existing offenses in untouched lib/factory_bot/definition.rb; this PR does not modify that file.