[Test] Make typecheck:dev green and gate tests/ + examples/ type-checking in CI

[pathosDev]

Use case

tests/ (299 files, ~3 578 tests) is excluded from tsconfig.json, and typecheck:dev — the config that would check tests/, examples/ and benchmarks/ — runs in no CI workflow and is currently red (~314 pre-existing errors). Bun executes tests without type-checking them, so type rot in the test suite accumulates invisibly, and the suite's types drift from the APIs they exercise.

Proposed approach

• Burn down the ~314 typecheck:dev errors (mostly mechanical: stale option shapes, missing generics on probes, as never remnants).
• Add bun run typecheck:dev as a CI job (own workflow or a job in test.yml) once green.
• Keep the build tsconfig untouched — this gates the dev config only.

Acceptance criteria

• bun run typecheck:dev exits 0 on develop
• CI job runs it on PRs and fails on regressions
• AGENTS.md verification-gates section updated to include it

Related

• Prerequisite for compiling examples/ in CI (examples gate issue, filed alongside)
• [Feature] Type-assertion debt: the ~197 remaining as-unknown-as / as-never sites #488 (type-assertion debt) — overlapping cleanup territory