Refactor node_offset range calculations to use get_node_range() interface

[milindsrivastava1997]

Problem

Many files still use manual instead of the proper and interface.

Violations Found

• generate_prometheus_config.py (lines 188, 221)
• experiment_utils/services/system_exporters.py (lines 40, 70, 92)
• experiment_utils/services/fake_exporters.py (multiple locations)
• experiment_utils/services/misc.py (lines 45, 68, 108)
• experiment_collect_prom_data.py (lines 44, 88, 154, 228)

Solution Options

1. Pass args object to services instead of separate node_offset/num_nodes params
2. Add helper methods to GeneratePrometheusArgs and service base classes

Context

Helper methods already exist in experiment_utils/config.py:357-381 in the Args class.

[milindsrivastava1997]

Originally by @linear[bot] on 2025-11-11:

PRO-277