feat(java): add async client and interface with CompletableFuture support

[jackye1995]

Summary

Add two new Java modules for async operations using Java 11+ native HttpClient:

• lance-namespace-async-client: Generated async HTTP client using library=native,asyncNative=true

  • Uses Java 11+ java.net.http.HttpClient
  • All API methods return CompletableFuture<T>

• lance-namespace-core-async: Async version of LanceNamespace interface

  • LanceNamespaceAsync interface mirroring LanceNamespace
  • All methods return CompletableFuture<T>
  • Includes async error classes

Key Changes

• Add async-client-pom.xml (copied after codegen, following Rust's pattern)
• Update Makefile with async client targets
• Update checkstyle-suppressions.xml for async client
• Update java-publish.yml to include async modules in Maven Central check

Usage

// Sync (existing)
LanceNamespace ns = LanceNamespace.connect("rest", props, allocator);
ListTablesResponse response = ns.listTables(request);

// Async (new)
LanceNamespaceAsync ns = LanceNamespaceAsync.connect("rest", props, allocator);
CompletableFuture<ListTablesResponse> future = ns.listTables(request);

Maven Dependencies

<!-- Async interface (Java 11+) -->
<dependency>
  <groupId>org.lance</groupId>
  <artifactId>lance-namespace-core-async</artifactId>
  <version>${version}</version>
</dependency>

<!-- Async client (Java 11+) -->
<dependency>
  <groupId>org.lance</groupId>
  <artifactId>lance-namespace-async-client</artifactId>
  <version>${version}</version>
</dependency>

Test plan

• make check passes (checkstyle + spotless)
• make build passes (all modules compile)
• CI workflows updated to include new modules

🤖 Generated with Claude Code