feat: seed mUSD as default tracked asset on mainnet, Linea, and Monad

[salimtb]

• Add defaults.ts with DEFAULT_TRACKED_ASSETS_BY_CHAIN, DEFAULT_ASSET_METADATA, buildDefaultAssetsInfo, getDefaultTrackedAssetsForChain, and getDefaultAssetMetadata
• Pre-seed assetsInfo in default controller state so mUSD is immediately renderable before any on-chain balance fetch completes
• Add #ensureDefaultTrackedAssetsSeeded to write zero-balance entries into assetsBalance for every EVM account on chains that have default tracked assets
• Wire seeding into controller start, account-tree changes, group changes, and enabled-network changes (passing only newly added chains to avoid redundant work)
• Subscribe to NetworkController:networkAdded and seed mUSD immediately when the user adds a chain that has default tracked assets (e.g. Monad testnet, eip155:143)
• Export all new helpers from index.ts
• Correct Monad chain id to eip155:143 (not eip155:10143)`

Explanation

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Introduces new default-asset seeding that mutates persisted controller state (assetsInfo/assetsBalance) on startup and in response to network/account events, which could affect token visibility and state size across chains/accounts if mis-scoped.

Overview
Adds controller-managed default tracked assets (mUSD) on eip155:1, eip155:59144, and eip155:143. Default controller state now pre-seeds assetsInfo with mUSD metadata so it is renderable before any fetch completes.

The controller now also seeds per-account zero balances for these defaults via #ensureDefaultTrackedAssetsSeeded, wired into startup, account-tree/group changes, enabled-network changes (only newly enabled chains), and a new NetworkController:networkAdded subscription to seed immediately when a supported network is added. A new defaults.ts registry and helpers are introduced and exported from index.ts, and tests/changelog are updated accordingly.

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