sdk(P1.5): on-chain anchor verification with zero heavy dependencies

verify_anchor_onchain / verifyAnchorOnchain / VerifyAnchorOnchain check an
anchor epoch against the chain itself in all three SDKs: one raw JSON-RPC
eth_call to the anchoring contract's getCommitment(batchId) comparing the
on-chain merkle root with the anchor's merkle_root, plus one
eth_getTransactionReceipt confirming status == 0x1 in the expected block.
The customer chooses the RPC endpoint — nothing asks Attesto to confirm
Attesto, and no web3/ethers dependency is added anywhere.

The getCommitment(string) selector (keccak256 first 4 bytes = a7b09e2a) is
pinned as a constant with the dynamic-string ABI encoding done manually;
a worked calldata example (computed once against web3 keccak) is asserted in
all three test suites, and APSProvenance.abi.json is copied into each SDK's
testdata with a test that flags the pinned selector for review if the ABI's
getCommitment signature ever changes. The contract address is read from the
anchor epoch's hashed payload (payload.contract_address).

Mocked-RPC tests cover match / root-mismatch / failed-tx / wrong-block /
missing-fields in each language with identical problem strings; a live test
against the production contract runs only when ATTESTO_LIVE_RPC_URL is set.
Go CLI gains `attesto anchors verify <id> --rpc-url <url>` (API fetch +
on-chain check in one step; existing get/remote-verify behavior unchanged).
READMEs updated per SDK.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

testdata/APSProvenance.abi.json

@@ -0,0 +1,172 @@
+[
+  {
+    "inputs": [],
+    "stateMutability": "nonpayable",
+    "type": "constructor"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      }
+    ],
+    "name": "AlreadyCommitted",
+    "type": "error"
+  },
+  {
+    "inputs": [],
+    "name": "EmptyBatchId",
+    "type": "error"
+  },
+  {
+    "inputs": [],
+    "name": "NotOwner",
+    "type": "error"
+  },
+  {
+    "anonymous": false,
+    "inputs": [
+      {
+        "indexed": true,
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      },
+      {
+        "indexed": true,
+        "internalType": "bytes32",
+        "name": "merkleRoot",
+        "type": "bytes32"
+      },
+      {
+        "indexed": false,
+        "internalType": "uint32",
+        "name": "runCount",
+        "type": "uint32"
+      },
+      {
+        "indexed": false,
+        "internalType": "string",
+        "name": "model",
+        "type": "string"
+      },
+      {
+        "indexed": false,
+        "internalType": "uint64",
+        "name": "blockTimestamp",
+        "type": "uint64"
+      }
+    ],
+    "name": "RootCommitted",
+    "type": "event"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "uint256",
+        "name": "",
+        "type": "uint256"
+      }
+    ],
+    "name": "batchIds",
+    "outputs": [
+      {
+        "internalType": "string",
+        "name": "",
+        "type": "string"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      },
+      {
+        "internalType": "bytes32",
+        "name": "merkleRoot",
+        "type": "bytes32"
+      },
+      {
+        "internalType": "uint32",
+        "name": "runCount",
+        "type": "uint32"
+      },
+      {
+        "internalType": "string",
+        "name": "model",
+        "type": "string"
+      }
+    ],
+    "name": "commitRoot",
+    "outputs": [],
+    "stateMutability": "nonpayable",
+    "type": "function"
+  },
+  {
+    "inputs": [],
+    "name": "getBatchCount",
+    "outputs": [
+      {
+        "internalType": "uint256",
+        "name": "",
+        "type": "uint256"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      }
+    ],
+    "name": "getCommitment",
+    "outputs": [
+      {
+        "internalType": "bytes32",
+        "name": "merkleRoot",
+        "type": "bytes32"
+      },
+      {
+        "internalType": "uint32",
+        "name": "runCount",
+        "type": "uint32"
+      },
+      {
+        "internalType": "string",
+        "name": "model",
+        "type": "string"
+      },
+      {
+        "internalType": "uint64",
+        "name": "blockTimestamp",
+        "type": "uint64"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
+  {
+    "inputs": [],
+    "name": "owner",
+    "outputs": [
+      {
+        "internalType": "address",
+        "name": "",
+        "type": "address"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  }
+]