Fix edge cases

This release fixes two timing bugs and raises unit and mutation test coverage for useTimer, useThrottleCallback and useThrottleEffect.

Fixes

useTimer — the timer no longer goes negative when crossing zero. The stop condition was a strict updatedSeconds === 0, so a fractional seconds count (e.g. useTimer(2.5) or restart(0.4)) never landed exactly on 0: active stayed true and count ran negative indefinitely. It now stops on updatedSeconds <= 0 with a clamp to 0, matching the existing pattern in decrease().
useThrottleCallback — a call arriving right after a trailing invocation no longer bypasses the throttle window. isCalledRef was reset unconditionally on every timer tick, so the next call saw isCalledRef === false and fired immediately instead of queuing, breaking the once-per-delay guarantee. The reset now happens only when there are no pending trailing calls, matching utils/helpers/throttle.ts. useThrottleState and useThrottleValue inherit the fix since both wrap useThrottleCallback.

Raised unit and mutation test coverage for useTimer, useThrottleCallback and useThrottleEffect.
Added new reactuse agent skills for React hooks best practices.