feat: support bunx for js configs

[nwidynski]

Description (What)

This change detects bun and when present uses bunx instead of npx for executing js-based config files.

Justification (Why)

Bun package installations may not be compatible with the npm task runner. This is the case when using a custom BUN_INSTALL_CACHE_DIR with the isolated linker setting.

How Can This Be Tested?

1. Setup a new bun repository
2. Configure a custom cache.dir and "isolated" linker setting via bunfig.toml
3. Add syncpack and a syncpack.config.ts
4. Attempt to run syncpack lint

Result: ✗ Node.js/npx/tsx process failed with stderr: sh: tsx: command not found

[JamieMason]

Thanks @nwidynski 👍