feat(cold-sql): add topic indexes for log filtering (#54)

* feat(cold-sql): add topic1/topic2/topic3 indexes for log filtering

Only topic0 was indexed previously. Most ERC-20/721 Transfer event
lookups filter on topic1 (from address) or topic2 (to address),
causing sequential scans on the logs table.

Adds migration 002 with indexes on all three remaining topic columns.
Uses CREATE INDEX IF NOT EXISTS for idempotent application.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: consolidate duplicate topic index migration

The 002 migration SQL is dialect-agnostic (CREATE INDEX IF NOT EXISTS),
so a single file suffices for both PostgreSQL and SQLite. Removes the
duplicate _pg variant and uses a shared include_str! outside the
backend match arm.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rswanson

crates/cold-sql/migrations/002_add_topic_indexes.sql

@@ -0,0 +1,9 @@
+-- Add indexes on topic1, topic2, topic3 for log filtering.
+--
+-- topic0 already has an index (001_initial). Most ERC-20/721
+-- Transfer lookups filter on topic1 (from) or topic2 (to), which
+-- previously required sequential scans.
+
+CREATE INDEX IF NOT EXISTS idx_logs_topic1 ON logs (topic1);
+CREATE INDEX IF NOT EXISTS idx_logs_topic2 ON logs (topic2);
+CREATE INDEX IF NOT EXISTS idx_logs_topic3 ON logs (topic3);

crates/cold-sql/src/backend.rs

@@ -127,6 +127,9 @@ impl SqlColdBackend {
         // Execute via pool to ensure the migration uses the same
         // connection that subsequent queries will use.
         sqlx::raw_sql(migration).execute(&pool).await?;
+        sqlx::raw_sql(include_str!("../migrations/002_add_topic_indexes.sql"))
+            .execute(&pool)
+            .await?;
         Ok(Self { pool, is_postgres })
     }