fix(dynamodb): avoid blocking IO inside Uni in DynamoDbIncrementRepository

[yuokada]

Background

Raised in PR #330 review (Copilot, comment r2936080069).

DynamoDbIncrementRepository.delete() and keys() return Uni<…> but internally call the synchronous DynamoDbClient, which blocks the calling thread. When these methods are invoked on an event-loop thread (e.g. from a reactive REST endpoint) this can stall the Vert.x event loop.

Affected methods

Method	Current client	Problem
delete(String key)	asyncClient.deleteItem(…)	OK — uses async client ✓
keys()	asyncClient.scan(…)	OK — uses async client ✓
get(String key)	client (sync)	Blocking — called from non-@Blocking context
set(String key, long value)	client (sync)	Blocking — called from non-@Blocking context
increment(String key, long by)	client (sync)	Blocking — called from non-@Blocking context

Expected fix

Either:

1. Annotate the resource/service methods that call get/set/increment with @Blocking, or
2. Switch get, set, increment to use DynamoDbAsyncClient and return Uni.

References

• PR feat: add DynamoDB support foundation (Phase 1) #330
• Quarkus docs: Execution model, blocking, non-blocking