fix: Add nullability annotations and fix kotlin-stdlib transitive leak

[obabichevjb]

Which Issue(s) This PR Fixes

• [Enhancement] Add Nullable annotations to nullable Message getters and fix kotlin-stdlib transitive leak #10978

Brief Description

This PR contains two independent fixes:

1. @Nullable annotations on 7 getters in Message.java that can return null at runtime. The methods are declared as returning plain String/Map with no nullability metadata, which produces silent NPEs in Kotlin consumers and gives no warning in Java IDEs.

2. Exclude leaked kotlin-stdlib from the opentelemetry-exporter-otlp dependency chain. A pure-Java project depending on rocketmq-client transitively resolves kotlin-stdlib via: opentelemetry-exporter-otlp → opentelemetry-exporter-sender-okhttp → okhttp → kotlin-stdlib-*. Upstream already wrote kotlin-stdlib exclusions for the okio-jvm edge; this extends them to cover the okhttp path, enforcing a constraint upstream already intended.

[RockteMQ-AI]

Summary

This PR adds @Nullable annotations to getter methods in Message.java that can legitimately return null, and excludes transitive kotlin-stdlib dependencies from opentelemetry-exporter-otlp to reduce dependency bloat.

Both changes look correct and well-scoped:

• The @Nullable annotations accurately reflect the nullability contract of these getters (e.g., getTags(), getKeys(), getTransactionId() can all return null)
• The kotlin-stdlib exclusions prevent unnecessary transitive dependencies from leaking into the classpath

LGTM.

---

Automated review by github-manager-bot