test(ci): add strict nextest ci profile with quarantine + flake policy
Formalize the existing ecstore-serial-flaky mechanism into a strict CI gate
(ci-10, absorbs infra-15; backlog#1149).
- .config/nextest.toml: add [profile.ci] with global retries=0 (never mask a
new race's first occurrence), fail-fast=false, and JUnit output at
target/nextest/ci/junit.xml. Add a quarantine section where flaky tests get
retries=2 under the ci profile only; each entry links one OPEN issue. First
members are the two backlog#937 ecstore groups
(concurrent_resend_same_part_commits_one_generation and
store::bucket::tests::bucket_delete_*), which keep their existing
ecstore-serial-flaky test-group serialization. Local default profile still
never retries.
- .github/workflows/ci.yml: run the main test step with --profile ci and upload
the JUnit report (if: always(), 3-day retention, run-number in name). The
migration-proof step stays on the default profile to avoid clobbering the ci
JUnit artifact (its tests are not quarantined).
- docs/testing/README.md: new skeleton (owned by backlog#1153 infra-11) holding
the flake policy: discover -> open issue within 24h -> quarantine with issue
link -> fix or delete within 30 days. AGENTS.md points to it.
Refs: rustfs/backlog#1149, rustfs/backlog#937, rustfs/backlog#1155
Zhengchao An