sandbox float resources

[kcoopermiller]

Note

Enables fractional resource specifications for sandboxes across SDK models and CLI.

• Change cpu_cores, memory_gb, disk_size_gb from int to float in models.py (Sandbox, CreateSandboxRequest, UpdateSandboxRequest) and update defaults
• Update CLI sandbox create options to accept floats for CPU/memory/disk
• Adjust format_resources to accept floats and display using :g for compact formatting

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