Non-blocking election initiator that returns immediately after registering
vote endpoints with iomgr and scheduling the election timeout watchdog.
- Single-node shortcircuit (n_peers==1): allocates self-only ha_elect_ctx_t,
calls ha_elect_evaluate_and_signal directly, frees ctx inline — no iomgr
or delaymgr involvement; returns in < 1ms
- Multi-node: allocates ha_elect_ctx_t, per-peer vote_ep_ctx_t, calls
endpoint_connect + iomgr_monitor for each peer; schedules election timeout
via delay_task_ms; skips peer on connect failure (counted as denied)
- election_timeout_fn: delaymgr callback that fires ha_elect_evaluate_and_signal
after election_timeout_ms, unless cancelled flag is set (lock-free cancellation)
- vote_ep_err_handler: counts unreachable peers as denied votes
- Declares ha_start_election_async in ha.h with full doc comment
- 5 Unity tests in test_ha_start_election_async.c: returns < 5ms, stores
n_peers, shortcircuit fires immediately, n_peers stored for multi-peer,
term incremented — all GREEN with ASAN enabled
