Shared TTL-memo utility with a test-reset registry for process-global caches #1042

Context

Six hand-rolled process-global caches exist today: runnerSessions, the simulator booted-memo (simulator.ts), the device-ready cache (device-ready.ts), runner idle-stop timers, the apple-tool fingerprint cache (runner-xctestrun.ts), and the device tunnel-IP cache (runner-transport.ts). Each reinvents TTL bookkeeping and its own __resetXForTests. This bug class fired three times in one week: booted-memo leaked across tests in index.test.ts (needed a hand-added reset), and two separate mock-reset omissions in session.test.ts (one caught by external review on #1025).

Expectation

A small src/utils/ttl-memo.ts (get/set/delete, TTL, unref'd timers where applicable) plus a module-level registry that a single shared test helper can reset (resetAllProcessMemosForTests()), wired into the common test setup so new memos are reset by construction. Migrate at least booted-memo, device-ready cache, and fingerprint cache to prove the shape; the rest can follow. Acceptance: no per-cache reset exports needed in new code; existing suites green; a test that deliberately leaks a memo across two tests fails without the registry reset and passes with it.