feat(consensus): add session registration protocol with combined login+register

[krishvishal]

Summary

• Add Operation::Register as a VSR-level operation that goes through consensus to create durable client sessions, giving each client a deterministic session number (= commit op number) agreed upon by all replicas.
• Add session field to RequestHeader with wire-layer validation: register requires session=0, request=0; all other operations require session>0, request>0.
• Split ClientTable into session-aware paths: check_register() / commit_register() for registration, and check_request() / commit_reply() with session + strict request monotonicity validation (NoSession, SessionMismatch, `RequestGap).
• Add ConsensusSession (SDK) for client-side session lifecycle and SessionManager (server-ng) for transport-to-consensus bridging.
• Add combined login_register handler: phase 1 verifies credentials locally, phase 2 submits register through consensus.
• Add RequestFrame2/ResponseFrame2 with request_id for request-response correlation and pipelining support.

[codecov]

Codecov Report

❌ Patch coverage is 91.68185% with 137 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.13%. Comparing base (6d44521) to head (e5012b2).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
core/metadata/src/impls/metadata.rs	43.85%	32 Missing ⚠️
core/server-ng/src/login_register.rs	88.80%	18 Missing and 10 partials ⚠️
core/consensus/src/client_table.rs	91.26%	12 Missing and 8 partials ⚠️
core/server-ng/src/session_manager.rs	90.14%	16 Missing and 4 partials ⚠️
core/partitions/src/iggy_partition.rs	70.58%	9 Missing and 1 partial ⚠️
core/binary_protocol/src/framing.rs	95.77%	0 Missing and 9 partials ⚠️
core/consensus/src/plane_helpers.rs	69.23%	8 Missing ⚠️
core/sdk/src/session.rs	97.19%	3 Missing ⚠️
core/simulator/src/lib.rs	95.83%	1 Missing and 1 partial ⚠️
...nary_protocol/src/requests/users/login_register.rs	99.25%	0 Missing and 1 partial ⚠️
... and 4 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3108      +/-   ##
============================================
+ Coverage     72.62%   73.13%   +0.51%     
  Complexity      943      943              
============================================
  Files          1117     1123       +6     
  Lines         96380    97892    +1512     
  Branches      73555    75082    +1527     
============================================
+ Hits          69997    71595    +1598     
+ Misses        23831    23682     -149     
- Partials       2552     2615      +63     

Components	Coverage Δ
Rust Core	74.02% <91.68%> (+0.69%)	⬆️
Java SDK	62.30% <ø> (ø)
C# SDK	69.13% <ø> (-0.28%)	⬇️
Python SDK	81.43% <ø> (ø)
Node SDK	91.31% <ø> (-0.10%)	⬇️
Go SDK	39.41% <ø> (ø)

Files with missing lines	Coverage Δ
core/binary_protocol/src/codes.rs	100.00% <ø> (ø)
core/binary_protocol/src/consensus/header.rs	80.56% <100.00%> (+4.60%)	⬆️
core/binary_protocol/src/consensus/operation.rs	95.18% <100.00%> (+0.81%)	⬆️
core/binary_protocol/src/dispatch.rs	91.15% <100.00%> (+0.15%)	⬆️
...nary_protocol/src/requests/users/login_register.rs	99.25% <99.25%> (ø)
...ocol/src/requests/users/login_register_with_pat.rs	99.18% <99.18%> (ø)
...ary_protocol/src/responses/users/login_register.rs	97.72% <97.72%> (ø)
core/consensus/src/observability.rs	40.18% <0.00%> (-0.10%)	⬇️
core/simulator/src/client.rs	52.60% <97.14%> (+10.04%)	⬆️
core/simulator/src/lib.rs	86.22% <95.83%> (+1.79%)	⬆️
... and 8 more

... and 28 files with indirect coverage changes

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[numinnex]

I've looked through this PR and I wonder how does it differ from the login and login with personal access token ?

[krishvishal]

@numinnex I've only implemented login functionality with register but didn't implement login with personal access token. But its easily implementable because register doesn't care about how we logged in.