Migrate to JSpecify annotations for nullability constraints #5547
Description
Deprecate our internal nullability annotations that are meta-annotated with JSR-305 annotations, add a dependency on JSpecify, update nullability imports and annotation usage to match correct use of JSpecify. See https://jspecify.dev/docs/using/
Breaking the work down into parts to make review more manageable:
- Migrate commons/observation modules to jSpecify #6158
- Migration to jSpecify (part 2) #6270
- Migrate Prometheus registries to jSpecify #6296
- Migrate micrometer-core to jSpecify #6385
- Migrate micrometer-observation and micrometer-observation-test to JSpecify #6420
- Migrate docs to JSpecify and apply formatting #6422