feat(config): moderate spawn tuning for Alex's Mobs, Fowl Play, Critters

Every visible entity multiplies the client render cost (vanilla, EMF/FA,
GeckoLib, ETF, dynamic lights) and the server tick. These cuts target only the
species that are heavy by weight x group size. Rare mobs keep their defaults.

- Alex's Mobs: halve 9 common weights (gazelle and capuchin herds, straddler,
  rocky roller, underminer, elephant, blobfish, mudskipper, caiman).
- Fowl Play: lower duck/goose/gull/sparrow weights and max group sizes
  (upstream #214, ~400 ducks on rivers, is still open in 1.2.3).
- Critters and Companions: about 40% off sea bunnies and the forest/lush bug
  rules. It does have a spawn config; configVersion 2 skips its v1->v2
  migration.

All three are partial files. NeoForge (TOML) and YACL 3.8.2 (JSON5) keep
defaults for missing keys. Shipped enforced from config/ because the server
reads them from this repo. Details and the B14 measurement plan:
analysis/client-perf/SPAWN-TUNING.md.

pack.toml

@@ -6,7 +6,7 @@ pack-format = "packwiz:1.1.0"
 [index]
 file = "index.toml"
 hash-format = "sha256"
-hash = "50d97b070e620b4e850df2feb7a07b11bf7a90cab87efa96219a217b9586446d"
+hash = "3c17e58506c00f8c5aba5151afa765fdd68245c384293a017a5e2062ac35afbe"
 
 [versions]
 minecraft = "1.21.1"