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 91.48936% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.59%. Comparing base (aff29a5) to head (1289d2e).

Files with missing lines	Patch %	Lines
.../apache/iggy/client/async/tcp/SystemTcpClient.java	86.48%	5 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 ⚠️
...ggy/client/async/tcp/ConsumerOffsetsTcpClient.java	92.59%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2718      +/-   ##
============================================
+ Coverage     68.52%   68.59%   +0.06%     
- Complexity      656      708      +52     
============================================
  Files           743      750       +7     
  Lines         62808    62996     +188     
  Branches      59221    59224       +3     
============================================
+ Hits          43039    43211     +172     
- Misses        17656    17671      +15     
- Partials       2113     2114       +1     

Flag	Coverage Δ
java	54.02% <91.48%> (+1.82%)	⬆️

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

Files with missing lines	Coverage Δ
...ache/iggy/client/async/tcp/AsyncIggyTcpClient.java	98.38% <100.00%> (+0.56%)	⬆️
...iggy/client/async/tcp/ConsumerGroupsTcpClient.java	68.11% <100.00%> (+52.73%)	⬆️
...che/iggy/client/async/tcp/PartitionsTcpClient.java	100.00% <100.00%> (ø)
...lient/async/tcp/PersonalAccessTokensTcpClient.java	100.00% <100.00%> (ø)
...org/apache/iggy/client/async/PartitionsClient.java	0.00% <0.00%> (ø)
...ggy/client/async/tcp/ConsumerOffsetsTcpClient.java	92.59% <92.59%> (ø)
...pache/iggy/client/async/ConsumerOffsetsClient.java	0.00% <0.00%> (ø)
...apache/iggy/client/async/ConsumerGroupsClient.java	0.00% <0.00%> (ø)
.../apache/iggy/client/async/tcp/SystemTcpClient.java	86.48% <86.48%> (ø)

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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

[atharvalade]

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

added some UTs, please check now. @ex172000 @mmodzelewski

[mmodzelewski]

before storing an offset you need to send some message to a stream, see the latest updates to the blocking client tests

[atharvalade]

oh yes you're right