Add millisecond-granularity delay_task_ms() to delaymgr using
clock_gettime(CLOCK_MONOTONIC) for deadline computation. Extends
delay_task_t with nextrun_ts field; delay_worker distinguishes
ms-tasks from second-tasks via non-zero nextrun_ts. Backward
compatible with existing delay_task callers.
4 delay tests pass (2 new: tolerance and invalid-args).
Provides the timeout primitive for election and committing watchdogs.
- Rename `precision` field to `precision_ms` in delaymgr_t struct (delay.h)
- Replace `sleep(mgr->precision)` with `nanosleep()` for 10ms granularity (delay.c)
- Add `#include <time.h>` to delay.c (already in delay.h)
- Update delaymgr_init() to store precision_ms parameter
- Update all call sites: cluster.c (2→200ms), controller/testsuite/test.c (2→2000ms),
lib/testsuite/test_delay.c (1→1000ms)
- Add TDD test test_delaymgr_precision_ms_field verifying field exists and stores correctly
- delay_task() delay parameter remains in seconds; only sleep granularity changes
