fix: fix keepalive SendRequest hang when connection is closed

[zx06]

Fix SSH keepalive SendRequest deadlock by wrapping it in a channel-based select with a timeout. Under the new version of golang.org/x/crypto, SendRequest might hang indefinitely if the connection is closed.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.00%. Comparing base (c773a13) to head (bfdd2c8).
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
internal/ssh/client.go	90.90%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #58       +/-   ##
===========================================
+ Coverage   47.02%   83.00%   +35.97%     
===========================================
  Files          16       46       +30     
  Lines        1412     3706     +2294     
===========================================
+ Hits          664     3076     +2412     
+ Misses        655      473      -182     
- Partials       93      157       +64     

Flag	Coverage Δ
e2e	47.02% <ø> (ø)
integration	47.02% <ø> (ø)
unittests	71.31% <90.90%> (?)

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