fix: bound compressor minContentLength before narrowing to uint32

[dxbjavid]

What this PR does / why we need it:

minContentLength on a compressor is a resource.Quantity, and its CRD pattern allows suffixes up to Ei, so the API server accepts values well above 4 GiB. buildCompression cast the parsed int64 straight to a uint32, which quietly wraps: 4Gi became 0, so Envoy compressed every response rather than only large ones, the opposite of what was configured (4Gi+30 lands on 30, and so on). This routes the value through the existing int64ToUint32 bounds check, the same helper the other numeric fields in this file already use, and surfaces a policy error for out-of-range values instead of silently truncating. The deprecated spec.compression[] path had the same cast and gets the same fix.

Which issue(s) this PR fixes:
Fixes #

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PR Checklist

• Authorship & ownership: Coding agents / AI assistants are welcome, but I have reviewed every change, understand how and why it works, can explain and maintain it, and take full responsibility for this PR. I have not submitted generated output I do not understand.
• DCO: All commits are signed off (git commit -s). See DCO: Sign your work.
• API agreed first: N/A: no API changes.
• Required checks pass: make lint and the unit tests for the touched package pass locally.
• Tests added/updated: added boundary and overflow cases to TestBuildCompression.
• Docs: N/A: no user-facing docs change.
• Release notes: added release-notes/current/bug_fixes/9852-compression-mincontentlength-overflow.md.
• Generated files committed: N/A: no API/helm/module changes.
• Scope & compatibility: scoped to the compression translation, behaviour for valid inputs is unchanged.
• Codex review: Requested a Codex review and addressed all of its comments.
• Copilot review: Requested a Copilot review and addressed all of its comments.

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[codecov]

Codecov Report

❌ Patch coverage is 82.60870% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.27%. Comparing base (3b80726) to head (d846148).

Files with missing lines	Patch %	Lines
internal/gatewayapi/backendtrafficpolicy.go	82.60%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9852      +/-   ##
==========================================
- Coverage   81.29%   81.27%   -0.02%     
==========================================
  Files         263      263              
  Lines       40859    40870      +11     
==========================================
+ Hits        33216    33218       +2     
- Misses       7643     7652       +9     

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[arkodg]

LGTM thanks

[apkatsikas]

This comment seems to be documenting the previously broken behavior as a justification for its existence. Maybe it could be tightened up.

// minContentLengthToUint32 converts the CRD quantity to the uint32 Envoy expects. 
// It rejects out-of-range values.

[zirain]

/retest