CI: split verify-tests #210

Follow-up to #208 (week 2). After the pull request checks were split into parallel jobs, verify-tests is the long pole: about 8.8 minutes, while every other check finishes within about 2 minutes.

Measured on run 43121035276:

• Unit specs (yarn test, Vitest): 350 s, about 6 minutes, more than half of it module import time.
• Client contract generation and checks: about 86 s.
• Library end-to-end tests: about 40 s.
• Decorator checks: a few seconds.

Scope

• Run the unit specs in their own job as disjoint Vitest shards (--shard=i/n), each shard required through the existing verify check.
• Keep client contract, decorator and Library end-to-end tests in verify-tests.
• Add a guard spec that fails when a command is dropped from the local yarn ci gate or a shard is missing from the matrix.

Acceptance criteria

• No check is removed from the pull request path; verify stays the required check name.
• yarn ci still runs every check locally.
• Pull request wall time drops from about 9 minutes to about 3-4 minutes.

Status

State: Done — Merged in #211; CI wall 9.1 -> 4.0 min.
Branch: fix/4906-repair-timing-options
Scope: Split unit specs into 3 Vitest shard jobs; deliver to L0 (no-release)
Plan: verify-tests keeps client contract, decorator and Library e2e checks; new verify-specs matrix job runs yarn test --shard=i/3; guard spec pins every original yarn ci command and the shard matrix; verify aggregate needs verify-specs.
Delivered: - #211
Remaining: To be confirmed.
Follow-ups: None.