fix(trace-logs): timestamp_precise is a number, not a string (#323)

Fixes a runtime Zod validation error when running `sentry trace logs`.
The trace-logs API returns `timestamp_precise` as a nanosecond integer
(same as Explore/Events logs), not an ISO string as originally assumed.

**Changes:**
- `TraceLogSchema.timestamp_precise`: `z.string()` → `z.number()`
- Updated JSDoc and test fixtures to match

Follow-up to #311.

Author: BYK