feat(shard): add v2 consumer-offset commands with AckLevel

[krishvishal]

Summary

• Introduce AckLevel { NoAck, Quorum } and v2 wire commands StoreConsumerOffset2 / DeleteConsumerOffset2 that carry an explicit ack byte; v1 commands and wire format are untouched.
• Unify the server's two offset-write paths so PollMessages auto-commit and explicit stores share a single shard entry point, with AckLevel selecting the policy.

[codecov]

Codecov Report

❌ Patch coverage is 67.15867% with 178 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.41%. Comparing base (fbf3885) to head (31cbb35).

Files with missing lines	Patch %	Lines
core/partitions/src/iggy_partition.rs	9.40%	106 Missing ⚠️
core/consensus/src/plane_helpers.rs	0.00%	41 Missing ⚠️
core/simulator/src/client.rs	0.00%	28 Missing ⚠️
core/consensus/src/observability.rs	0.00%	2 Missing ⚠️
core/binary_protocol/src/primitives/ack_level.rs	97.61%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3151      +/-   ##
============================================
- Coverage     74.46%   74.41%   -0.05%     
  Complexity      943      943              
============================================
  Files          1183     1186       +3     
  Lines        105866   106343     +477     
  Branches      82899    83393     +494     
============================================
+ Hits          78835    79138     +303     
- Misses        24289    24433     +144     
- Partials       2742     2772      +30     

Components	Coverage Δ
Rust Core	75.69% <67.15%> (-0.06%)	⬇️
Java SDK	60.14% <ø> (ø)
C# SDK	69.07% <ø> (-0.31%)	⬇️
Python SDK	81.43% <ø> (ø)
Node SDK	91.53% <ø> (ø)
Go SDK	39.60% <ø> (ø)

Files with missing lines	Coverage Δ
core/binary_protocol/src/codes.rs	100.00% <ø> (ø)
core/binary_protocol/src/consensus/operation.rs	96.11% <100.00%> (+0.15%)	⬆️
core/binary_protocol/src/dispatch.rs	91.45% <100.00%> (+0.30%)	⬆️
...uests/consumer_offsets/delete_consumer_offset_2.rs	100.00% <100.00%> (ø)
...quests/consumer_offsets/store_consumer_offset_2.rs	100.00% <100.00%> (ø)
core/consensus/src/client_table.rs	93.72% <100.00%> (ø)
core/binary_protocol/src/primitives/ack_level.rs	97.61% <97.61%> (ø)
core/consensus/src/observability.rs	37.26% <0.00%> (-0.18%)	⬇️
core/simulator/src/client.rs	45.27% <0.00%> (-7.33%)	⬇️
core/consensus/src/plane_helpers.rs	82.01% <0.00%> (-7.07%)	⬇️
... and 1 more

... and 24 files with indirect coverage changes

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[numinnex]

This command suppose to be implemented only in the components that are used by the cluster which is in development, not by our core server.