Add disk IO to resources output

[sjmiller609]

Note

Low Risk
Primarily adds new output fields and formatting logic; risk is limited to display correctness and compatibility if the server response lacks disk_io fields.

Overview
Adds disk I/O capacity and per-instance allocation reporting to hypeman resources table output, including a new DISK I/O column and disk_io row.

Introduces formatDiskBps to display disk bandwidth in bytes/sec (KB/s, MB/s, GB/s) distinct from network bit-rate formatting, with accompanying unit tests.

Bumps github.com/kernel/hypeman-go from v0.9.3 to v0.9.6 to pick up the API/client support for the new disk_io fields.

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