Change addGeneratedAnnotationDate default to false #44

Change the default value of addGeneratedAnnotationDate from true to false for the next major version.

This makes builds reproducible and cacheable by default, removing the non-deterministic timestamp from @Generated annotations.

Files to update

• MappingConfigConstants.java: DEFAULT_ADD_GENERATED_ANNOTATION_DATE = false
• docs/codegen-options.md: update default value column
• Tests: update expected outputs that currently include the date