feat(e2b): add sandbox refresh endpoint

[vishwas-droid]

Fixes #506

Summary

This change adds support for the E2B-compatible sandbox refresh endpoint:

POST /sandboxes/{sandboxID}/refreshes

The endpoint allows clients to refresh a sandbox's TTL without modifying other lifecycle operations.

What Changed

• Added RefreshSandboxRequest model with duration field.
• Added RefreshSandbox handler.
• Registered the new /sandboxes/{sandboxID}/refreshes route.
• Reused existing timeout utilities to keep refresh behavior consistent with the rest of the E2B lifecycle implementation.
• Preserved existing never-timeout sandbox behavior.
• Applied ExtendOnly timeout updates to avoid shortening an existing longer deadline.

Tests

Added coverage for:

• Invalid duration requests.
• Refreshing a non-existent sandbox.
• Refreshing a running sandbox updates its timeout.
• Never-timeout sandboxes remain unchanged after refresh.

Validation

CGO_ENABLED=0 go test ./pkg/servers/e2b/...

[kruise-bot]

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[kruise-bot]

Welcome @vishwas-droid! It looks like this is your first PR to openkruise/agents 🎉

[codecov]

Codecov Report

❌ Patch coverage is 80.55556% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.63%. Comparing base (96be268) to head (f18086c).

Files with missing lines	Patch %	Lines
pkg/servers/e2b/refresh.go	80.00%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #512   +/-   ##
=======================================
  Coverage   78.63%   78.63%           
=======================================
  Files         181      182    +1     
  Lines       12879    12915   +36     
=======================================
+ Hits        10127    10156   +29     
- Misses       2374     2379    +5     
- Partials      378      380    +2     

Flag	Coverage Δ
unittests	78.63% <80.55%> (+<0.01%)	⬆️

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[vishwas-droid]

CC-@furykerry @zmberg @AiRanthem PTAL!