chore: add uranium and natgas icons

[gambinish]

Add URNM and NATGAS icons

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Note

Low Risk
Low risk: adds new static metadata JSON entries and corresponding SVG icons only, with no changes to runtime logic. Main risk is incorrect symbol/name/logo paths affecting asset resolution.

Overview
Adds two new hip3 asset definitions for xyz:NATGAS (Henry Hub Natural Gas) and xyz:URNM (Sprott Uranium Miners ETF), each with decimals: 6 and a logo path.

Includes the corresponding new SVG logo files under icons/eip155:999/hip3/ for both assets.

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