feat(picod): add gzip middleware for response compression

[Abhinav-kodes]

What type of PR is this?

/kind enhancement
/kind feature

What this PR does / why we need it:
This PR implements Gzip compression for the PicoD daemon, fulfilling one of the planned network enhancements in the picod-proposal.md design doc.

By injecting the gin-contrib/gzip middleware, the PicoD server can now perform on-the-fly compression for HTTP responses. This drastically reduces network bandwidth and improves latency for large data transfers, such as retrieving bulky stdout/stderr payloads from /api/execute or downloading large text/JSON files via /api/files/*path.

The middleware uses standard content negotiation:

• Clients requesting Accept-Encoding: gzip will receive compressed payloads.
• Clients not supporting compression will seamlessly fall back to plain text.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

• Downgraded gin-contrib/gzip explicitly to v1.0.1 to maintain compatibility with the project's Go 1.24.4 toolchain, avoiding unintended transitive upgrades to Go 1.25.0+.
• Uses gzip.DefaultCompression (level 6) to provide the optimal balance between high compression ratios and low CPU overhead.
• All existing tests pass, as compression is completely transparent to the application logic.

Does this PR introduce a user-facing change?:

Added Gzip compression support to the PicoD daemon to significantly improve file transfer and command execution speeds over constrained networks.

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[gemini-code-assist]

Code Review

This pull request introduces Gzip response compression to the Gin server by adding the github.com/gin-contrib/gzip dependency and registering it as global middleware. Feedback suggests optimizing the compression level to BestSpeed to reduce CPU overhead and excluding the /health endpoint from compression to avoid unnecessary processing for small responses.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.14%. Comparing base (524e55e) to head (3f3db68).
⚠️ Report is 54 commits behind head on main.
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #339      +/-   ##
==========================================
+ Coverage   47.57%   49.14%   +1.57%     
==========================================
  Files          30       30              
  Lines        2819     2859      +40     
==========================================
+ Hits         1341     1405      +64     
+ Misses       1338     1301      -37     
- Partials      140      153      +13     

Flag	Coverage Δ
unittests	49.14% <100.00%> (+1.57%)	⬆️

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