Implement SQLite WAL mode and performance optimizations

## Description
Add WAL (Write-Ahead Logging) mode support and various SQLite performance optimizations.

## Requirements
- [ ] WAL mode configuration
- [ ] PRAGMA optimizations
- [ ] Connection pooling for SQLite
- [ ] Prepared statement caching
- [ ] Vacuum and maintenance operations
- [ ] Write comprehensive tests

## Acceptance Criteria
- WAL mode support with configuration
- Automatic PRAGMA optimizations
- Efficient connection reuse
- Maintenance operation support

## Files to modify
- `beatrix_core/src/relational/db/sqlite.rs`
- `beatrix_core/src/relational/pool.rs`

## Example Usage
```rust
let db = SQLite::new("database.db")
.wal_mode(true)
.cache_size(64 * 1024) // 64MB cache
.optimize_for_writes()
.connect().await?;

// Periodic maintenance
db.vacuum().await?;
db.analyze().await?;
```