Summary

• restore the default job key serialization format used before the JobParameter refactor
• avoid relying on JobParameter.toString for key generation to keep key values stable
• add a regression test in DefaultJobKeyGeneratorTests for backward-compatible key generation
• add a JDBC DAO regression test to verify lookup of existing job instances created with the legacy key format

Testing

• ./mvnw -pl spring-batch-core -Dtest=DefaultJobKeyGeneratorTests,JdbcJobInstanceDaoTests test

Fixes #5283