[FEAT] expose original sanbox instance

[Diluka]

Is your feature request related to a problem? Please describe.

    const e2bSandbox: Sandbox = await sandbox['getSandbox']();
    const bytes = await e2bSandbox.files.read(quotedPath, { format: 'bytes' });

I want to use e2b sandbox api

Describe alternatives you've considered

No response

Additional context

No response

Describe the thing to improve

Now I use the private api to get any type instance

[omeraplak]

Opened a PR for this: #1068

It adds public getSandbox() accessors for both E2BSandbox and DaytonaSandbox, plus docs and changesets.

Would you like to review it now?