ci: parallelize coverage across two BVT groups

[XuPeng-SH]

What this PR does / why we need it

Reworks PR coverage collection to remove the serial UT + full-BVT critical path while retaining Race UT and coverage breadth.

• adds a separate non-race UT coverage producer; Race UT remains unchanged and does not block coverage merge
• uses exactly two active BVT jobs: Compose + Proxy and Launch + Pessimistic
• splits every non-optimistic BVT case into two complementary, timing-balanced groups; each run executes both groups once and a rerun swaps their deployment mapping
• collects profiles in the producer jobs and merges exactly one UT plus two BVT profiles
• skips merge when any producer fails, coverage secrets are unavailable, the PR is untrusted, or the PR is a draft
• routes Compose SQL through Proxy and gracefully stops coverage-instrumented services
• compacts the all-package UT profile before upload, reducing the observed artifact from about 622 MB to 3,519,245 bytes without changing merged block/hit results
• fixes production object-storage retry cancellation and bounds QCloud multipart abort cleanup to 30 seconds
• propagates test deadlines through object-storage constructors and operations so a remote outage cannot consume the package-level 10-minute timeout
• adds the production entrypoint calls for Coverage UT and Coverage Merge; the same entrypoint disables legacy coverage atomically

Rollout dependency

Depends on matrixorigin/CI#404. Merge CI#404 first. Its enable_legacy_coverage input defaults to true, so the old entrypoint retains legacy coverage until this PR merges; this PR passes false in the same commit that enables the new producers.

.github/workflows/coverage-integration.yaml is validation-only and pins reviewed CI commit 6beb8d8bb8a93d62f6ff02591c3eafe287d536ce. Remove it after the final integration run passes and before merging this PR.

Which issue(s) this PR fixes:

Related performance issue: #25116

Validation

• pkg/fileservice: full short package test passed
• pkg/fileservice: full short -race test passed; final changed-helper race selection passed
• go vet ./pkg/fileservice: passed
• make err-check: passed
• actionlint on MatrixOne entrypoint/integration workflows: passed
• actionlint on changed CI coverage workflows: passed (known custom runner labels excluded)
• BVT grouping: 1,113 non-optimistic scripts; group union/disjoint validation passed
• Docker Compose launch-multi-cn config validation: passed
• CI workflow schema validation in ci: split coverage into parallel producers CI#404: passed

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