22: Add dummy AnchorIdlJupiterPerpsCustodyDecoder.decodeCurrentCumulativeInterestRate() method

src/main/tjava/com/r35157/libs/jupiter/perps/impl/anchoridl/AnchorIdlJupiterPerpsCustodyDecoder.tjava

@@ -4,6 +4,7 @@ import com.r35157.libs.codec.Base58Codec;
 import com.r35157.libs.codec.impl.ref.Base58CodecImpl;
 import com.r35157.libs.solana.SolanaAccountInfo;
 
+import java.math.BigInteger;
 import java.util.Base64;
 
 class AnchorIdlJupiterPerpsCustodyDecoder {
@@ -22,6 +23,10 @@ class AnchorIdlJupiterPerpsCustodyDecoder {
         return readPublicKey(data, MINT_OFFSET);
     }
 
+    BigInteger decodeCurrentCumulativeInterestRate(SolanaAccountInfo custodyAccountInfo) {
+        return null;
+    }
+
     private ΩSPLMintAddressΩ readPublicKey(
             byte[] data,
             int offset
@@ -42,9 +47,22 @@ class AnchorIdlJupiterPerpsCustodyDecoder {
     private static final int ANCHOR_DISCRIMINATOR_LENGTH = 8;
     private static final int PUBLIC_KEY_LENGTH = 32;
 
-    private static final int MINT_OFFSET =
-            ANCHOR_DISCRIMINATOR_LENGTH
-                    + PUBLIC_KEY_LENGTH; // pool
+    // Offsets:
+    //    8   discriminator
+    //   +32 pool
+    //   +32 mint
+    //   +32 token_account
+    //   +1  decimals
+    //   +1  is_stable
+    //   +45 oracle
+    //   +48 pricing
+    //   +7  permissions
+    //   +8  target_ratio_bps
+    //   +48 assets
+
+    private static final int MINT_OFFSET = ANCHOR_DISCRIMINATOR_LENGTH + PUBLIC_KEY_LENGTH;
+    private static final int FUNDING_RATE_STATE_OFFSET = 262;
+    private static final int CUMULATIVE_INTEREST_RATE_OFFSET = FUNDING_RATE_STATE_OFFSET;
 
     private static final Base58Codec base58 = new Base58CodecImpl();
 }