CAMEL-22640: Add JSpecify null safety annotations to camel-api

[gnodet]

Summary

Add JSpecify null safety annotations to the camel-api module, following the same approach adopted by Spring Framework 7 / Spring Boot 4.

• Add org.jspecify:jspecify:1.0.0 dependency to parent POM (dependencyManagement) and camel-api
• Add @NullMarked to all 16 packages in camel-api via package-info.java, making non-null the default
• Annotate ~200 API interfaces and classes with @Nullable where parameters or return values can legitimately be null
• Covers the full API surface: CamelContext, Exchange, Message, Component, Endpoint, TypeConverter, ProducerTemplate, ConsumerTemplate, all SPI interfaces, vault configs, JSE support, health checks, etc.

This establishes the convention and pattern for Camel null safety. Follow-up PRs can extend coverage to camel-support, camel-core-model, and individual components.

JIRA: https://issues.apache.org/jira/browse/CAMEL-22640

[github-actions]

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