abi2: expose array index when decoding abi arrays (#191)

E2PG copies N rows where N is equal to the number of elements in an abi
encoded array(s). For example, if you have the following type:

	X(uint8,uint8[2])

then, assuming no filters, 2 rows will be inserted into the table. Each
row will have the first uint8 and the 1 and 2nd row will have the 0th
and 1st element of the abi encoded array respectively.

This change allows the integration to request the array index be copied
into the row. Continuing the example, given the following bytes:

	000000000000000000000000000000000000000000000000000000000000002a
	0000000000000000000000000000000000000000000000000000000000000040
	0000000000000000000000000000000000000000000000000000000000000002
	000000000000000000000000000000000000000000000000000000000000002b
	000000000000000000000000000000000000000000000000000000000000002c

the following rows will be inserted:

	 abi_idx | a  | b
	---------+----+----
	       0 | 42 | 43
	       1 | 42 | 44

E2PG decodes a log which contains an abi array, (eg an array of
structs or an array of uint256s)

abi2/abi2.go

@@ -775,9 +775,15 @@ func (ig Integration) processLog(rows [][]any, lwc *logWithCtx) ([][]any, error)
 					row[j] = dbtype(def.Input.Type, d)
 					ictr++
 				case !def.BlockData.Empty():
-					d := lwc.get(def.BlockData.Name)
-					if b, ok := d.([]byte); ok && !def.BlockData.Accept(b) {
-						return rows, nil
+					var d any
+					switch {
+					case def.BlockData.Name == "abi_idx":
+						d = i
+					default:
+						d = lwc.get(def.BlockData.Name)
+						if b, ok := d.([]byte); ok && !def.BlockData.Accept(b) {
+							return rows, nil
+						}
 					}
 					row[j] = d
 				default:

e2pg/integration_test.go

@@ -120,24 +120,27 @@ func TestIntegrations(t *testing.T) {
 				where order_hash = '\xdaf50b59a508ee06e269125af28e796477ebf55d22a3c6a24e42d038d9d8d8ee'
 				and tx_hash = '\x713df81a2ab53db1d01531106fc5de43012a401ddc3e0586d522e5c55a162d42'
 				and log_idx = 3
-				and offer_token is null
-				and consideration_recipient = '\x5e97a8773122bde31d44756f271c87893991a6ea'
+				and abi_idx = 0
+				and offer_token = '\x57f1887a8bf19b14fc0df6fd9b2acc9af147ea85'
+				and consideration_recipient is null
 				`,
 				`
 				select true from seaport_test
 				where order_hash = '\xdaf50b59a508ee06e269125af28e796477ebf55d22a3c6a24e42d038d9d8d8ee'
 				and tx_hash = '\x713df81a2ab53db1d01531106fc5de43012a401ddc3e0586d522e5c55a162d42'
 				and log_idx = 3
+				and abi_idx = 1
 				and offer_token is null
-				and consideration_recipient = '\x0000a26b00c1f0df003000390027140000faa719'
+				and consideration_recipient = '\x5e97a8773122bde31d44756f271c87893991a6ea'
 				`,
 				`
 				select true from seaport_test
 				where order_hash = '\xdaf50b59a508ee06e269125af28e796477ebf55d22a3c6a24e42d038d9d8d8ee'
 				and tx_hash = '\x713df81a2ab53db1d01531106fc5de43012a401ddc3e0586d522e5c55a162d42'
 				and log_idx = 3
-				and offer_token = '\x57f1887a8bf19b14fc0df6fd9b2acc9af147ea85'
-				and consideration_recipient is null
+				and abi_idx = 2
+				and offer_token is null
+				and consideration_recipient = '\x0000a26b00c1f0df003000390027140000faa719'
 				`,
 			},
 		},

e2pg/testdata/seaport.json

@@ -12,14 +12,16 @@
 			{"name": "recipient", "type": "bytea"},
 			{"name": "block_num", "type": "numeric"},
 			{"name": "tx_hash", "type": "bytea"},
-			{"name": "log_idx", "type": "numeric"}
+			{"name": "log_idx", "type": "numeric"},
+			{"name": "abi_idx", "type": "numeric"}
 		]
 	},
 	"block": [
 		{"name": "chain_id", "column": "chain_id"},
 		{"name": "block_num", "column": "block_num"},
 		{"name": "tx_hash", "column": "tx_hash", "filter_op": "contains", "filter_arg": ["713df81a2ab53db1d01531106fc5de43012a401ddc3e0586d522e5c55a162d42"]},
-		{"name": "log_idx", "column": "log_idx"}
+		{"name": "log_idx", "column": "log_idx"},
+		{"name": "abi_idx", "column": "abi_idx"}
 	],
 	"event": {
 		"anonymous": false,