Potential race condition - JdbcTaskRepository#memoize

[NicklasWallgren]

There is a risk that initialized is cached between threads, leading to multiple initializations.

Explaination;

1. Thread 1 calls get and enters the firstTime method.
2. Before firstTime completes, Thread 2 calls get.
3. Since initialized might not be updated yet (due to thread interleaving), Thread 2 might also enter the firstTime method.
4. Both threads could end up calling the original supplier and setting delegate and initialized, leading to multiple initializations.

Fix; Make initialized and delegate volatile to ensure visibility across threads.