feat(csharp): implement rented message polling

[lukaszzborek]

Rationale

Polling path allocated fresh byte[] per message payload + another per raw user-headers blob. On high-throughput consumers that's dominant allocation source. Goal: cut allocs by reusing pooled buffers, without breaking existing safe API.

What changed

• Underlying poll now reads server bytes into MemoryPool.Shared.Rent(...) buffer instead of new byte[len]. Whole batch shares one rented buffer; payloads + raw headers are slices into it.
• New rented polling path: IggyConsumer.ReceiveRentedAsync() yields ReceivedRentedMessage. Slices stay alive until caller disposes. Saves 1–2 allocs per message vs old path.
• Typed variant: IggyConsumer.ReceiveDeserializedAsync() deserializes whole batch eagerly, returns buffer to pool immediately. Caller disposes nothing.
• New client method: IIggyClient.PollMessagesRentedAsync(...) → PolledMessagesRental.
• IDeserializer.Deserialize signature: byte[] → ReadOnlyMemory.
• Old ReceiveMessagesAsync / MessageResponse API unchanged on surface, but internally also reads into pooled buffer now and materializes byte[] only after mapping — saves 1 allocation per poll (the big receive buffer).

What's next

• Move encryption/decryption into IggyClient so it stops re-allocating (TODO in IggyConsumer.Rented.cs:158).
• Add rented / Memory / Span API on send path.
• Make header mapping lazy after decryption move.
• Update docs in iggy website repo.

Benchmark in comment

[codecov]

Codecov Report

❌ Patch coverage is 76.81661% with 134 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.44%. Comparing base (f1965fc) to head (7207260).

Files with missing lines	Patch %	Lines
...n/csharp/Iggy_SDK/Consumers/IggyConsumer.Rented.cs	60.71%	46 Missing and 9 partials ⚠️
...SDK/IggyClient/Implementations/TcpMessageStream.cs	81.64%	9 Missing and 20 partials ⚠️
foreign/csharp/Iggy_SDK/Consumers/IggyConsumer.cs	37.50%	16 Missing and 4 partials ⚠️
...reign/csharp/Iggy_SDK/Contracts/MessageResponse.cs	68.96%	9 Missing ⚠️
...n/csharp/Iggy_SDK/Consumers/IggyConsumerBuilder.cs	0.00%	3 Missing and 1 partial ⚠️
...csharp/Iggy_SDK/Consumers/ReceivedRentedMessage.cs	86.66%	3 Missing and 1 partial ⚠️
...oreign/csharp/Iggy_SDK/IggyClient/IIggyConsumer.cs	0.00%	4 Missing ⚠️
foreign/csharp/Iggy_SDK/Mappers/BinaryMapper.cs	95.65%	1 Missing and 3 partials ⚠️
...reign/csharp/Iggy_SDK/Consumers/IggyConsumerOfT.cs	94.87%	0 Missing and 2 partials ⚠️
...csharp/Iggy_SDK/Contracts/RentedMessageResponse.cs	94.11%	0 Missing and 1 partial ⚠️
... and 2 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3250      +/-   ##
============================================
+ Coverage     74.07%   74.44%   +0.37%     
  Complexity      943      943              
============================================
  Files          1201     1204       +3     
  Lines        110672   109354    -1318     
  Branches      87563    85944    -1619     
============================================
- Hits          81977    81407     -570     
+ Misses        25939    25176     -763     
- Partials       2756     2771      +15     

Components	Coverage Δ
Rust Core	75.74% <ø> (+0.48%)	⬆️
Java SDK	58.44% <ø> (ø)
C# SDK	70.12% <76.81%> (+0.68%)	⬆️
Python SDK	81.43% <ø> (ø)
Node SDK	91.44% <ø> (-0.10%)	⬇️
Go SDK	39.91% <ø> (ø)

Files with missing lines	Coverage Δ
...reign/csharp/Iggy_SDK/Consumers/ReceivedMessage.cs	100.00% <100.00%> (+16.66%)	⬆️
.../csharp/Iggy_SDK/Contracts/PolledMessagesRental.cs	100.00% <100.00%> (ø)
...DK/IggyClient/Implementations/HttpMessageStream.cs	72.02% <100.00%> (+0.29%)	⬆️
...csharp/Iggy_SDK/Contracts/RentedMessageResponse.cs	94.11% <94.11%> (ø)
.../csharp/Iggy_SDK/Extensions/IggyClientExtension.cs	0.00% <0.00%> (ø)
...ggy_SDK/JsonConverters/MessageResponseConverter.cs	70.90% <87.50%> (+2.90%)	⬆️
...reign/csharp/Iggy_SDK/Consumers/IggyConsumerOfT.cs	96.49% <94.87%> (+96.49%)	⬆️
...n/csharp/Iggy_SDK/Consumers/IggyConsumerBuilder.cs	74.12% <0.00%> (-2.14%)	⬇️
...csharp/Iggy_SDK/Consumers/ReceivedRentedMessage.cs	86.66% <86.66%> (ø)
...oreign/csharp/Iggy_SDK/IggyClient/IIggyConsumer.cs	50.00% <0.00%> (-50.00%)	⬇️
... and 5 more

... and 44 files with indirect coverage changes

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[hubcio]

/ready

[lukaszzborek]

Some benchmark:

Method	0.8.0 Mean	Current Mean	Δ Mean	0.8.0 Gen0	Current Gen0	0.8.0 Gen1	Current Gen1	0.8.0 Gen2	Current Gen2	0.8.0 Allocated	Current Allocated	Δ Allocated
PollMessagesAsync	22.52 ms	20.26 ms	-10.03%	312.5000	187.5000	312.5000	31.2500	312.5000	-	3.91 MB	2.97 MB	-24.04%
PollMessagesRentedAsync	22.52 ms*	22.56 ms	+0.18%	312.5000*	125.0000	312.5000*	-	312.5000*	-	3.91 MB*	1.93 MB	-50.64%
ConsumerReceiveAsync	24.15 ms	22.57 ms	-6.54%	312.5000	187.5000	312.5000	31.2500	312.5000	-	3.97 MB	3.02 MB	-23.93%
ConsumerReceiveRentedAsync	24.15 ms*	23.32 ms	-3.44%	312.5000*	125.0000	312.5000*	-	312.5000*	-	3.97 MB*	2 MB	-49.62%
TypedConsumerReceiveAsync	24.31 ms	22.57 ms	-7.16%	312.5000	125.0000	312.5000	31.2500	312.5000	-	4.02 MB	2 MB	-50.25%

* Compared against the 0.8.0 non-rented equivalent (PollMessagesAsync / ConsumerReceiveAsync) as requested.

It was tested with a 1 KB message. Polling messages were performed in batches of 100 until 1,000 processed messages were obtained (deserialising the messages via MessagePack).

[lukaszzborek]

/ready