Feature Request: Add Support for Bun SQL Driver in PostGraphile

### Feature description

Add support for Bun's native SQL driver (`Bun.SQL`) in PostGraphile. This would allow PostGraphile to leverage Bun's high-performance database connectivity when running in the Bun runtime environment.

Bun.SQL is a unified SQL API introduced in Bun 1.2+ that provides native database connectivity for PostgreSQL, MySQL, and SQLite with significantly better performance than traditional Node.js database drivers.

Key aspects of this feature:
- Integration of Bun.SQL as an alternative database driver option in PostGraphile
- Support for PostgreSQL through Bun's native implementation
- Leverage Bun's performance advantages for database operations
- Maintain compatibility with existing PostGraphile features while using the Bun driver

### Motivating example

**Performance Benefits:**
According to Bun's benchmarks, Bun.SQL demonstrates substantial performance improvements:
- Up to 6x faster than Node.js `postgres` package for high-concurrency workloads
- Lower latency and higher throughput in database operations
- More efficient memory usage compared to traditional drivers

**Development Experience:**
- Unified development stack when using Bun as the runtime
- Simplified dependency management by using Bun's built-in capabilities
- Better integration with Bun's tooling ecosystem

**Use Cases:**
1. **High-performance applications** that require maximum database throughput
2. **Bun-based projects** seeking to leverage native capabilities
3. **New greenfield projects** using modern JavaScript runtimes

### Breaking changes

This feature should not introduce breaking changes to existing PostGraphile installations. It would be implemented as:

- An optional driver that only activates when explicitly configured
- Additional configuration option for the database connection
- Fallback to existing drivers when not using Bun runtime

Potential considerations:
- Feature parity verification between Bun.SQL and existing PostgreSQL drivers
- Testing across different Bun versions to ensure compatibility
- Handling of Bun-specific connection parameters and configuration

https://bun.com/docs/runtime/sql

### Supporting development

I [tick all that apply]:

- [ ] am interested in building this feature myself
- [x] am interested in collaborating on building this feature
- [x] am willing to help testing this feature before it's released
- [ ] am willing to write a test-driven test suite for this feature (before it exists)
- [ ] am a [Graphile sponsor](https://www.graphile.org/sponsor/) ❤️
- [ ] have an active [support or consultancy contract](https://www.graphile.org/support/) with Graphile