internal/envoy: always set NumRetries so numRetries=-1 actually disables retries

[SAY-5]

Summary

HTTPProxy documents numRetries: -1 as "disable retries". The DAG translator in internal/dag/policy.go already maps the API value -1 to the DAG value 0 (with DAG value 1 standing for the default one-retry behaviour).

internal/envoy/v3/route.retryPolicy, however, only forwarded NumRetries to Envoy when the DAG value was > 0. When a user set numRetries: -1, the DAG value 0 silently disappeared from the Envoy RetryPolicy, and Envoy's documented default of 1 kicked in, giving exactly one retry instead of none.

Fix

Always set NumRetries (including 0) so the Envoy config matches what the API promised.

Fixes #5944.

Test

• go build ./internal/envoy/... green.
• go test ./internal/envoy/v3/... -count=1 -short passes.
• go test ./internal/xdscache/v3/... -count=1 -short passes (TestRouteVisit goldens unchanged).

Release Note

Fix `numRetries: -1` on HTTPProxy retry policies so it disables retries as documented, instead of falling back to Envoy's default of one retry.

/kind bug
/area httpproxy

[SAY-5]

Updated PR body with a release-note section per the template (I cannot self-apply the release-note/small label as a non-maintainer). go test ./internal/envoy/v3/... ./internal/xdscache/v3/... passes locally on this branch, TestRouteVisit goldens are unchanged by the NumRetries fix. Awaiting maintainer ok-to-test for the workflow run.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.32%. Comparing base (a94de15) to head (7f23167).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7525      +/-   ##
==========================================
- Coverage   82.32%   82.32%   -0.01%     
==========================================
  Files         130      130              
  Lines       15624    15622       -2     
==========================================
- Hits        12863    12861       -2     
  Misses       2478     2478              
  Partials      283      283              

Files with missing lines	Coverage Δ
internal/envoy/v3/route.go	92.84% <100.00%> (-0.02%)	⬇️
internal/featuretests/v3/envoy.go	99.34% <100.00%> (-0.01%)	⬇️

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