test: Add unit tests for metrics utilities

[alfieprojectsdev]

Added unit tests for services/vadase-rt-monitor/src/utils/metrics.py covering compute_horizontal_magnitude, convert_m_to_mm, convert_mm_to_m, and compute_3d_magnitude. Tests cover standard inputs, zero values, negative values, and floating point precision.

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PR created automatically by Jules for task 5465521941459795677 started by @alfieprojectsdev

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