WhatsApp debounced text for 5s (10s near a split) and Weixin for 3s/5s
before dispatching, so every reply paid multiple seconds of idle latency
that Telegram never pays (0.3s/1.0s). Default both adapters to Telegram's
cadence and mirror its ceilings (2.0s / 4.0s, split >= base delay) via the
existing _coerce_float_extra seam. The config keys are unchanged; 0 still
dispatches immediately. Docs updated.
Spotted via #44896 (@liuhao1024). Fixes#44883, refs #25056.