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

db/migrations/00029_create_header_sync_logs_table.sql

@@ -0,0 +1,21 @@
+-- +goose Up
+-- SQL in this section is executed when the migration is applied.
+CREATE TABLE header_sync_logs
+(
+    id           SERIAL PRIMARY KEY,
+    header_id    INTEGER NOT NULL REFERENCES headers (id) ON DELETE CASCADE,
+    address      VARCHAR(66),
+    topics       BYTEA[],
+    data         BYTEA,
+    block_number BIGINT,
+    block_hash   VARCHAR(66),
+    tx_hash      VARCHAR(66),
+    tx_index     INTEGER,
+    log_index    INTEGER,
+    raw          JSONB,
+    UNIQUE (header_id, tx_index, log_index)
+);
+
+-- +goose Down
+-- SQL in this section is executed when the migration is rolled back.
+DROP TABLE header_sync_logs;