Migrate to JSpecify annotations

[sh-cho]

(Base: #6457)

Motivation:
jsr-305 is dormant and now JSpecify is recommended annotation sets for variety of static analyses (for now, it supports only nullness) and many open sources are moving to JSpecify (e.g. Spring Framework, Guava, ...)

• https://jspecify.dev/
• https://spring.io/blog/2025/03/10/null-safety-in-spring-apps-with-jspecify-and-null-away

Modifications:

• Add JSpecify dependency
• Deprecate internal annotations and replace to JSpecify annotations
  • com.linecorp.armeria.common.annotation.Nullable -> org.jspecify.annotations.NullMarked
  • com.linecorp.armeria.common.annotation.NonNullByDefault -> org.jspecify.annotations.Nullable

Note:
Since JSpecify's Nullable annotation is type-use annotation, placement of existing jsr-305 annotations are incompatible with JSpecify one, so following steps should be applied (ref: https://jspecify.dev/docs/using/#if-your-code-already-uses-jsr-305-annotations)

• @Nullable Object[] -> Object @Nullable []
• @Nullable Map.Entry<K, V> -> Map.@Nullable Entry<K, V>

Result:

• Resolves Use JetBrains's Java annotations? #2793
• jsr-305 annotations are migrated

[github-actions]

🔍 Build Scan® (commit: a03482b)

Job name	Status	Build Scan®
build-ubicloud-standard-16-jdk-8	❌ (failure)	https://ge.armeria.dev/s/gl7xt7p3zn5oy
build-ubicloud-standard-16-jdk-21-snapshot-blockhound	❌ (failure)	https://ge.armeria.dev/s/by53lwhumrfxu
build-ubicloud-standard-16-jdk-17-min-java-17-coverage	❌ (failure)	https://ge.armeria.dev/s/rnsb5mbrubpyk
build-ubicloud-standard-16-jdk-17-min-java-11	❌ (failure)	https://ge.armeria.dev/s/gcxqaeym25l2e
build-ubicloud-standard-16-jdk-17-leak	❌ (failure)	https://ge.armeria.dev/s/odlccl2jsx7ay
build-ubicloud-standard-16-jdk-11	❌ (failure)	https://ge.armeria.dev/s/uiu6k4mmzbqf2
build-macos-latest-jdk-21	❌ (failure)	https://ge.armeria.dev/s/j23gxyrv5xaou

[sh-cho]

Need to sort out commits
-> rebase done

[sh-cho]

I'll open this after #6457 gets merged and rebased