crawler: split sleep policy by host — chain blob fetches drop 5s -> 0.2s

The Pro modern fetch_pro_modern walks a per-history blob loop on
modules.lceda.cn (CDN-flavored host serving AES-encrypted EPRO2 streams).
We were sleeping 5s between every blob — same rate we use for the
rate-sensitive pro.lceda.cn API host. HAR analysis (proexportNew2.har)
shows the editor fires these blobs back-to-back without throttling, so
0.2s is plenty.

Walltime drops linearly with chain length:
  ESP-VoCat (chain=12):    80s sleep -> 22s sleep  (-72%)
  220V power (chain=28):  160s sleep -> 26s sleep  (-84%)
  X86 board  (chain~700, projection):  ~1h -> ~3min

Verified by re-fetching ESP-VoCat + 220V power: byte-identical output
across all per-doc .epro2 files (sha256 match), only fetched_at
timestamp differs in manifest.json. Two manifest files re-stamped as
proof of the validation runs.

API host sleeps (4x 5s in modern fetcher, 7x 5s in legacy fetcher) are
unchanged — those go to pro.lceda.cn /api/ which still wants polite
QPS<=0.2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

data/raw/oshwhub/dc91a91e669349898d709a5ba02f5b5f/source/manifest.json

@@ -2,7 +2,7 @@
   "project_uuid": "dc91a91e669349898d709a5ba02f5b5f",
   "branch_uuid": "248807156ba341efb886f33121486d41",
   "head_uuid": "320b5e8efc184b6f92fae0adc05ff547",
-  "fetched_at": "2026-04-28T13:34:08.163913+00:00",
+  "fetched_at": "2026-04-28T16:08:04.447128+00:00",
   "editor_version": "3.2.69",
   "chain_length": 28,
   "blob_bytes_total": 7712204,