fix: update Jackson imports for Spring Boot 4.0 / Jackson 3.0 compatibility

[Copilot]

Spring Boot 4.0 bundles Jackson 3.0, which relocated its core package namespace from com.fasterxml.jackson to tools.jackson, breaking compilation.

Changes

• ProductMessageBuilder.java — update ObjectMapper and exception imports:

  // Before
  import com.fasterxml.jackson.core.JsonProcessingException;
  import com.fasterxml.jackson.databind.ObjectMapper;
  
  // After
  import tools.jackson.core.JacksonException;
  import tools.jackson.databind.ObjectMapper;

• ProductRepository.java — update catch (JsonProcessingException e) → catch (JacksonException e)
• ProductsKafkaProducerTest.java — update throws JsonProcessingException → throws JacksonException

com.fasterxml.jackson.annotation.JsonFormat in ProductEvent.java is unchanged — jackson-annotations 2.20 retains the com.fasterxml.jackson.annotation namespace in Jackson 3.0.

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