test(utils): svg_parser + device_info + default_assets (+14 tests)

[TaprootFreak]

Summary

Stage 22 of the coverage push. Pure-Dart utility files.

File	Cases
`lib/packages/utils/svg_parser.dart`	5
`lib/packages/utils/device_info.dart`	5
`lib/packages/utils/default_assets.dart`	4

What each file covers

• svg_parser: integer + decimal mm → px conversion at 96 DPI (≈ 3.7795 px/mm), non-mm units pass through unchanged, every `mm` occurrence is replaced (multiple per string), surrounding SVG markup is preserved.
• device_info: iOS / Android / macOS / Windows+Linux / Fuchsia matrix using `debugDefaultTargetPlatformOverride` (save + restore around each test so a failure doesn't leak the override).
• default_assets: mainnet `realUnitAsset` and Sepolia `realUnitTestAsset` pinned to their production / dev contract addresses + decimals + symbols (a typo here would silently route the entire fiat pipeline at the wrong contract). ETH and ZCHF asset-id constants also pinned.

Test plan

• `flutter analyze` clean
• `flutter test` — 14 / 14 passing locally
• CI green