fix(ci): increase test-partition timeout to 420m for cold cache builds

Cold debug build + 1/3 partition test execution observed at 300m+ on VPS2
(14 CPU, 28GB RAM). First pipeline after a Cargo.lock change triggers a cold
CACHE_KEY rebuild (~180-190m), leaving insufficient time for test execution.
420m provides headroom for cold-cache pipelines; warm cache runs complete in
45-90m well within the limit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -421,10 +421,10 @@ cargo-audit:
     - find /cache/cargo-target/"${CACHE_KEY}" -mindepth 1 -maxdepth 1 -type d ! -name "test-release" -exec rm -rf {} + 2>/dev/null || true
     - echo "CARGO_TARGET_DIR=$CARGO_TARGET_DIR (disk $(df -h /cache/cargo-target | tail -1 | awk '{print $3 "/" $2 " used, " $4 " free"}'))"
   cache: []
-  # 300m: cold debug build on VPS can still take 2-3h (first run after cache change).
-  # Warm cache completes in ~45m. Debug mode compiles 2-3x faster than --release
-  # while -Cdebug-assertions=y (set in RUSTFLAGS) keeps the same assertion coverage.
-  timeout: 300m
+  # 420m: cold debug build + full partition test run observed at 300m+. Warm cache
+  # (subsequent runs) completes in ~45-90m. The extra headroom avoids false timeout
+  # failures on the first pipeline after a Cargo.lock change (new CACHE_KEY).
+  timeout: 420m
   retry:
     max: 1
     when: