feat(java): add async API parity with blocking client

[atharvalade]

Which issue does this PR close?

Closes #2716

Rationale

The async TCP client was missing 17 methods that existed in the blocking client, limiting its usability for async workflows.

What changed?

The async TCP client only exposed 5 of 9 sub-client interfaces (Messages, ConsumerGroups, Streams, Topics, Users), and ConsumerGroupsClient had only 2 of 6 methods. This left 17 methods unavailable for async operations.

Added 4 new async client interfaces (SystemClient, PersonalAccessTokensClient, PartitionsClient, ConsumerOffsetsClient) with full TCP implementations, and extended ConsumerGroupsClient with 4 missing methods (get, getAll, create, delete). All async methods follow the existing pattern using CompletableFuture and match the blocking client API exactly.

Local Execution

• Passed
• Yes

AI Usage

1. Which tools? Claude Sonnet 4.5
2. Scope of usage? Code scaffolding and implementation assistance, AI helped generate the async client interfaces and TCP implementations following existing codebase patterns
3. How verified? Compiled successfully with Gradle build, reviewed all generated code against blocking client implementations to ensure correct serialization/deserialization logic, command codes, and error handling
4. Can explain every line? Yes, all code follows established patterns from existing async clients (UsersTcpClient, ConsumerGroupsTcpClient). Each implementation uses BytesSerializer for request payloads, CommandCode enums for operations, and BytesDeserializer for responses with proper resource cleanup in finally blocks.

[codecov]

Codecov Report

❌ Patch coverage is 10.63830% with 168 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.14%. Comparing base (2728100) to head (979b2d8).

Files with missing lines	Patch %	Lines
...iggy/client/async/tcp/ConsumerGroupsTcpClient.java	0.00%	43 Missing ⚠️
...lient/async/tcp/PersonalAccessTokensTcpClient.java	10.52%	34 Missing ⚠️
.../apache/iggy/client/async/tcp/SystemTcpClient.java	10.81%	33 Missing ⚠️
...ggy/client/async/tcp/ConsumerOffsetsTcpClient.java	14.81%	23 Missing ⚠️
...che/iggy/client/async/tcp/PartitionsTcpClient.java	22.22%	14 Missing ⚠️
...ache/iggy/client/async/tcp/AsyncIggyTcpClient.java	25.00%	12 Missing ⚠️
...apache/iggy/client/async/ConsumerGroupsClient.java	0.00%	4 Missing ⚠️
...pache/iggy/client/async/ConsumerOffsetsClient.java	0.00%	3 Missing ⚠️
...org/apache/iggy/client/async/PartitionsClient.java	0.00%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (10.63%) is below the target coverage (50.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2718      +/-   ##
============================================
- Coverage     68.32%   68.14%   -0.18%     
- Complexity      656      664       +8     
============================================
  Files           741      748       +7     
  Lines         62158    62346     +188     
  Branches      58571    58574       +3     
============================================
+ Hits          42468    42488      +20     
- Misses        17583    17751     +168     
  Partials       2107     2107              

Flag	Coverage Δ
java	50.26% <10.63%> (-1.94%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...org/apache/iggy/client/async/PartitionsClient.java	0.00% <0.00%> (ø)
...pache/iggy/client/async/ConsumerOffsetsClient.java	0.00% <0.00%> (ø)
...apache/iggy/client/async/ConsumerGroupsClient.java	0.00% <0.00%> (ø)
...ache/iggy/client/async/tcp/AsyncIggyTcpClient.java	79.03% <25.00%> (-18.80%)	⬇️
...che/iggy/client/async/tcp/PartitionsTcpClient.java	22.22% <22.22%> (ø)
...ggy/client/async/tcp/ConsumerOffsetsTcpClient.java	14.81% <14.81%> (ø)
.../apache/iggy/client/async/tcp/SystemTcpClient.java	10.81% <10.81%> (ø)
...lient/async/tcp/PersonalAccessTokensTcpClient.java	10.52% <10.52%> (ø)
...iggy/client/async/tcp/ConsumerGroupsTcpClient.java	5.79% <0.00%> (-9.59%)	⬇️

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[mmodzelewski]

Hi @atharvalade, thanks for the PR. It looks like some C# changes have accidentally slipped into this PR. Would you mind tidying up the diff so it only shows the Java updates? Once that's sorted, I'll start the review.

[atharvalade]

Hi @atharvalade, thanks for the PR. It looks like some C# changes have accidentally slipped into this PR. Would you mind tidying up the diff so it only shows the Java updates? Once that's sorted, I'll start the review.

Hi @mmodzelewski, thanks for catching that! I've rebased the branch onto the latest upstream master and removed the stray C# commit.

[ex172000]

It's probably a better idea we add some UT to the change, or even better if ingestion test can be added too. Otherwise our coverage is likely adversely impacted