Modernize demo dependencies and runtime cleanup

[adrianmilne]

Motivation

• Bring the project up-to-date for modern JVM/tooling by targeting Java 11 and newer Spring/JUnit versions and removing fragile legacy configuration in pom.xml.
• Fix runtime resource/lifecycle issues: close Spring context, stop executor threads, wait for generators to finish, and ensure Esper provider/statements are torn down to avoid leaks.
• Improve correctness and maintainability of the event model and observability by making TemperatureEvent immutable with defensive copies and adjusting logging severities for alert types.

Description

• Update pom.xml to target Java 11, bump Spring to 5.3.34, add JUnit 5 and modern Maven plugins and maven-surefire-plugin to enable tests and modern compilation behavior.
• Revise the demo entrypoint StartDemo to validate arguments (parseNumberOfEvents), use try-with-resources for ClassPathXmlApplicationContext, and wait for the generator Future to complete.
• Change RandomTemperatureEventGenerator to return a Future<?>, use ThreadLocalRandom, handle interruptions properly, and shut down the single-thread executor when finished.
• Harden TemperatureEvent by making it final, using final fields, performing defensive copies of Date values, and adding equals/hashCode.
• Add Esper lifecycle cleanup by implementing DisposableBean in TemperatureEventHandler and destroying created EPStatements and the EPServiceProvider in destroy().
• Adjust logging severities for subscribers so critical events use LOG.error, warnings use LOG.warn, and monitor output uses LOG.info.
• Add a unit test src/test/java/com/cor/cep/event/TemperatureEventTest.java that verifies defensive copying of the timestamp.

Testing

• Ran mvn test in the environment but the build failed due to inability to download a Maven plugin from Maven Central (HTTP 403), so tests could not be executed here; the new JUnit 5 test file was added but not run successfully under the constrained environment.

---

Codex Task