refactor(l2): improve SQL store initialization

[ManuelBilbao]

Motivation

Migrations of SQL schema are tricky. If new tables were added, it has to be migrated manually.

Description

Make SQL schema setup sentences idempotent so they can be executed on every start up.

[Copilot]

Pull request overview

This PR refactors the SQL store initialization to make it idempotent by adding IF NOT EXISTS clauses to all CREATE TABLE statements and ON CONFLICT DO NOTHING clauses to INSERT statements. This allows the schema setup to be executed on every startup without requiring manual migrations when new tables are added.

Key changes:

• All CREATE TABLE statements now use IF NOT EXISTS to prevent errors on re-execution
• Initial INSERT statements for operation_count and latest_sent tables now use ON CONFLICT DO NOTHING to avoid duplicate key errors
• Removed the check for existing tables before running schema setup, allowing the idempotent schema statements to run unconditionally

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[Copilot]

PRAGMA journal_mode=WAL is a write operation that modifies the database configuration, but it's being executed using self.query() which uses the read-only connection (read_conn). This should use self.execute() instead, which uses the write_conn connection. While this may work in some SQLite implementations, it could lead to "database is locked" errors or permission issues as mentioned in the comment on line 19.

Suggested change

	self.query("PRAGMA journal_mode=WAL;", ()).await?;
	self.execute("PRAGMA journal_mode=WAL;", ()).await?;

[github-actions]

Lines of code report

Total lines added: 0
Total lines removed: 8
Total lines changed: 8

Detailed view

+----------------------------------------------+-------+------+
| File                                         | Lines | Diff |
+----------------------------------------------+-------+------+
| ethrex/crates/l2/storage/src/store_db/sql.rs | 906   | -8   |
+----------------------------------------------+-------+------+