Write event logs to database before transforming

- enables decoupling event extraction/persistence from transformation
- modifies event transformer, converter, and log chunker to accept
  payload that includes internal log database ID with log data
- remove alias for transformer pkg as shared_t
- remove unused mock watcher repository

pkg/core/log.go

@@ -16,6 +16,8 @@
 
 package core
 
+import "github.com/ethereum/go-ethereum/core/types"
+
 type Log struct {
 	BlockNumber int64
 	TxHash      string
@@ -24,3 +26,10 @@ type Log struct {
 	Index int64
 	Data  string
 }
+
+type HeaderSyncLog struct {
+	ID          int64
+	HeaderID    int64 `db:"header_id"`
+	Log         types.Log
+	Transformed bool
+}