Clean up instance timeout handling

[chrisx9z]

Summary

• Ensures start() timeouts reject through the returned promise and reset the instance back to idle.
• Prevents the original start task from flipping the instance to started after the timeout has already fired.
• Clears timeout timers on successful start/stop paths and adds a patch changeset.

Fixes #44.

Verification

• corepack pnpm install --ignore-scripts
• corepack pnpm exec tsc --noEmit
• corepack pnpm exec biome check src/Instance.ts src/Instance.test.ts .changeset/soft-rings-sip.md
• corepack pnpm exec vitest src/Instance.test.ts --run
• git diff --check

Note

• vitest src/Instance.test.ts --run passes with 12 tests. It also reports existing warnings for two older .rejects assertions in unrelated tests that are not awaited.
• Local Windows pnpm build currently fails because zile tries to spawn node_modules/.bin/tsc without the .CMD extension; the focused test was run after generating a local dist with tsc for package resolution.