fix: pace inter-tier polling; fix stale package-rename references in docs

ocf/poll_scheduler.py

@@ -3,8 +3,8 @@
 Tiers are descriptor-declared (hot/warm/cold + sweep). Per tick:
 each tier whose deadline has passed polls all its paths sequentially
 on the shared session, writing into the StateCache. The sweep tier
-issues one Block2 GET of /device/0 and uses index_links to fan its
-result into many href reps.
+issues one Block2 GET of /device/0 and uses
+StateCache.index_device_tree to fan its result into many href reps.
 
 Adaptive cadence: when descriptor.is_active(cache.links) returns True
 and tier.active_interval_s is set, that tier uses the tighter cadence.
@@ -218,11 +218,13 @@ class PollScheduler:
     def _do_tier(self, tier: PollTier) -> None:
         timeout = self._tier_timeout(tier)
         cooldown = self._cooldown_for(tier)
-        for path in tier.paths:
+        for i, path in enumerate(tier.paths):
             href = '/' + '/'.join(path)
             with self._defer_lock:
                 if self._defer_until.get(href, 0) > time.monotonic():
                     continue
+            if i > 0:
+                self.session.pace()
             self._poll_count += 1
             t0 = time.monotonic()
             try: