feat(csharp): add VSR framing to the csharp SDK

[lukaszzborek]

The .NET SDK only spoke classic TCP framing, so it could not talk to
the clustered next-generation server.

Add runtime-selectable VSR framing via WireProtocol.Vsr, with the
register handshake, session lifetime tied to the connection, request
sequencing, bounded reply decoding, transient replays, leader
redirection over the cluster roster, and assignment-based consumer
groups.

The IIggyClient surface is unchanged. Partitioning moves client-side
(balanced and message-key, hash byte-compatible with the Rust SDK),
credentials are bounds-checked before framing, and a request written
without a server verdict surfaces as VsrRequestOutcomeUnknownException
rather than being silently replayed on a new session, since that would
bypass server-side deduplication.

[codecov]

Codecov Report

❌ Patch coverage is 85.86957% with 221 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.06%. Comparing base (102484a) to head (e948728).

Files with missing lines	Patch %	Lines
...IggyClient/Implementations/TcpMessageStream.Vsr.cs	73.51%	109 Missing and 25 partials ⚠️
...SDK/IggyClient/Implementations/TcpMessageStream.cs	85.61%	12 Missing and 9 partials ⚠️
.../Iggy_SDK/Publishers/BackgroundMessageProcessor.cs	24.00%	18 Missing and 1 partial ⚠️
...gn/csharp/Iggy_SDK/Vsr/ConsumerGroupClientState.cs	86.98%	15 Missing and 4 partials ⚠️
foreign/csharp/Iggy_SDK/Utils/ServerAddress.cs	89.47%	2 Missing and 4 partials ⚠️
foreign/csharp/Iggy_SDK/Vsr/VsrOperation.cs	96.09%	2 Missing and 3 partials ⚠️
foreign/csharp/Iggy_SDK/Vsr/LoginRegister.cs	94.59%	2 Missing and 2 partials ⚠️
foreign/csharp/Iggy_SDK/Vsr/VsrHeader.cs	94.91%	2 Missing and 1 partial ⚠️
...DK/Exceptions/VsrRequestOutcomeUnknownException.cs	0.00%	2 Missing ⚠️
foreign/csharp/Iggy_SDK/Consumers/IggyConsumer.cs	50.00%	0 Missing and 1 partial ⚠️
... and 7 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3800      +/-   ##
============================================
+ Coverage     75.96%   76.06%   +0.10%     
  Complexity      969      969              
============================================
  Files          1320     1334      +14     
  Lines        157608   159079    +1471     
  Branches     130990   131248     +258     
============================================
+ Hits         119720   121008    +1288     
- Misses        34297    34345      +48     
- Partials       3591     3726     +135     

Components	Coverage Δ
Rust Core	75.96% <ø> (-0.01%)	⬇️
Java SDK	62.71% <ø> (ø)
C# SDK	75.07% <85.86%> (+2.81%)	⬆️
Python SDK	93.10% <ø> (ø)
PHP SDK	84.52% <ø> (ø)
Node SDK	95.30% <ø> (+0.07%)	⬆️
Go SDK	43.08% <ø> (ø)

Files with missing lines	Coverage Δ
...csharp/Iggy_SDK/Configuration/AutoLoginSettings.cs	100.00% <100.00%> (ø)
...p/Iggy_SDK/Configuration/IggyClientConfigurator.cs	100.00% <100.00%> (ø)
...n/csharp/Iggy_SDK/Consumers/IggyConsumer.Rented.cs	69.29% <100.00%> (-2.50%)	⬇️
...n/csharp/Iggy_SDK/Consumers/IggyConsumerBuilder.cs	74.35% <100.00%> (-5.65%)	⬇️
...gn/csharp/Iggy_SDK/Consumers/IggyConsumerConfig.cs	100.00% <100.00%> (ø)
...y_SDK/Exceptions/IggyInvalidStatusCodeException.cs	100.00% <100.00%> (ø)
.../Iggy_SDK/Exceptions/VsrSessionEvictedException.cs	100.00% <100.00%> (ø)
...reign/csharp/Iggy_SDK/Factory/IggyClientFactory.cs	94.28% <100.00%> (-0.72%)	⬇️
...csharp/Iggy_SDK/Publishers/IggyPublisherBuilder.cs	50.24% <100.00%> (+1.53%)	⬆️
.../csharp/Iggy_SDK/Publishers/IggyPublisherConfig.cs	100.00% <100.00%> (ø)
... and 20 more

... and 40 files with indirect coverage changes

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