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 71.72%. Comparing base (b55d065) to head (d3f5b66).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3032      +/-   ##
============================================
- Coverage     71.74%   71.72%   -0.03%     
  Complexity      930      930              
============================================
  Files          1121     1103      -18     
  Lines         93777    91606    -2171     
  Branches      71125    68920    -2205     
============================================
- Hits          67284    65706    -1578     
+ Misses        23856    23449     -407     
+ Partials       2637     2451     -186     

Components	Coverage Δ
Rust Core	72.32% <ø> (-0.02%)	⬇️
Java SDK	62.08% <ø> (ø)
C# SDK	67.64% <ø> (ø)
Python SDK	81.43% <ø> (ø)
Node SDK	91.44% <ø> (-0.10%)	⬇️
Go SDK	39.09% <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 154 files with indirect coverage changes

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