Modify bandwidth-test to use command-line tool execution

[devin-ai-integration]

Modify bandwidth-test to use command-line tool execution

This PR modifies the bandwidth-test tool to use external process execution instead of embedded service creation. The changes:

1. Created a new Process struct to manage external command execution
2. Modified runBandwidthTest to launch ffts/fftw/fft as separate processes
3. Simplified send.go and recv.go to remove embedded implementation
4. Added verbose flag to control output display from external processes
5. Improved error handling and process management

These changes decouple the bandwidth-test from the core code, simulating direct user operations by launching independent processes.

Link to Devin run: https://app.devin.ai/sessions/11f53f3220ba460ca53ff68829597d60
Requested by: fatedier

[devin-ai-integration]

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