fix(core): refresh EffectFlock heartbeats on every tick - #51181

Issue for this PR

Closes #51179

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

EffectFlock.acquire started its heartbeat with fs.utimes(path, new Date(), new Date()) piped into Effect.repeat. The repeat reruns that same effect, so both dates stay at the time the lock was acquired and the heartbeat never moves forward. Once a lock has been held for 60 s, isStale treats it as abandoned, and another process can break it while the holder is still working, for example during a slow npm install or a repository clone.

Wrapping the call in Effect.suspend builds a new utimes effect on each tick, so each tick writes the current time. The rest of the heartbeat fiber is unchanged: same schedule, still scoped to the lock and interrupted before release.

How did you verify your code works?

New test in packages/core/test/util/effect-flock.test.ts: acquire a lock, backdate its heartbeat by 120 s, wait 1 s of wall time, advance the TestClock by one heartbeat interval, then check the heartbeat's age. Before the fix it fails (age 1058 ms, the acquisition time); after it, it passes. bun test test/util/effect-flock.test.ts passes (12 pass, 0 fail) and bun typecheck is clean in packages/core.

Screenshots / recordings

n/a

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR