Fix Search traces with min/max duration with timeunits

[ksankeerth]

• before this fix, siglens doesn't have support for searching with time duration of different units
• If search example 'search latency>0.5ms' would fail with errors
• the fix avoids converting time duration with units to string

Description

• Before convert values like "10s", "10ms", "10ds", "10cs" to string directly, PEG grammer will try to convert as time duration. If that fails only, they will be converted to String
• Added new evaluation struct TimeDuration and some additional grammer rules for avoid string conversions for time duration
• Moved and modified GetIntervalInMillis function to different file for reusing

Fixes #574

Testing

• added tests

Checklist:

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