fix(go): update stats field and its deserialization logic to align with rust SDK

[chengxilo]

Which issue does this PR close?

Address #2964 (comment)

Rationale

The rust side now serializes threads_count, free_disk_space, and total_disk_space on the wire (in core/server/src/binary/mapper.rs), but the go Stats struct (foreign/go/contracts/stats.go) and its deserializer (foreign/go/binary_serialization/stats_serializer.go) don't read these fields.

(Yeah, I copied the comment) 😋

What changed?

1. Adds attributes to Stats, also the tests.
2. Removed TcpStats and update the function related to it as Stats is already enough for our logic.
3. Refactor Stats deserialization logic with reader introduced in feat(go): implement binary reader/writer #2986

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

1. Claude Opus 4.6
2. Code generation and review.
3. I checked it with the rust implementation of stats.
4. Yes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.68%. Comparing base (051475a) to head (5809769).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3032      +/-   ##
============================================
+ Coverage     70.52%   70.68%   +0.16%     
  Complexity      943      943              
============================================
  Files          1115     1113       -2     
  Lines         95388    94495     -893     
  Branches      72589    71663     -926     
============================================
- Hits          67275    66798     -477     
+ Misses        25634    25230     -404     
+ Partials       2479     2467      -12     

Components	Coverage Δ
Rust Core	70.75% <ø> (+0.18%)	⬆️
Java SDK	62.30% <ø> (ø)
C# SDK	69.40% <ø> (ø)
Python SDK	81.43% <ø> (ø)
Node SDK	91.53% <ø> (+0.12%)	⬆️
Go SDK	39.37% <100.00%> (+0.40%)	⬆️

Files with missing lines	Coverage Δ
foreign/go/client/tcp/tcp_utilities.go	80.00% <100.00%> (ø)
foreign/go/contracts/stats.go	100.00% <100.00%> (ø)

... and 35 files with indirect coverage changes

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