chore(spartan): lower mainnet inactivity slash target to 70%

Reduce the mainnet SLASH_INACTIVITY_TARGET_PERCENTAGE default from 0.8
(80%) to 0.7 (70%) in spartan/environments/network-defaults.yml. Only
the networks.mainnet preset is changed; devnet/testnet and the top-level
slasher anchor (all 0.9) are untouched.

(cherry picked from commit 71f8e3d)

Author: aminsammara

spartan/environments/network-defaults.yml

@@ -365,7 +365,7 @@ networks:
     ENABLE_AUTO_SHUTDOWN: false
     # Slasher penalties - more lenient initially
     SLASH_DATA_WITHHOLDING_PENALTY: 0
-    SLASH_INACTIVITY_TARGET_PERCENTAGE: 0.8
+    SLASH_INACTIVITY_TARGET_PERCENTAGE: 0.7
     SLASH_INACTIVITY_CONSECUTIVE_EPOCH_THRESHOLD: 2
     SLASH_INACTIVITY_PENALTY: 2000e18
     SLASH_PROPOSE_INVALID_ATTESTATIONS_PENALTY: 2000e18