feat(account-tree-controller): add import support

[ccharly]

Explanation

Add the export functions for the import/export feature of the account-tree.

References

• feat(account-tree-controller)!: add {import,export}State actions #9663

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

High Risk
Import decodes mnemonics and private keys and drives keyring/multichain wallet creation; mistakes could corrupt vault state or mishandle secrets.

Overview
Adds importState to apply a deserialized AccountTreeSnapshot to local account-tree state, complementing the existing export path.

For mnemonic wallets, it matches wallets by stable entropy payload ID (via keyring), creates HD wallets through MultichainAccountService when a mnemonic is present, batches missing account groups with createMultichainAccountGroups, and applies wallet/group metadata (name, pinned, hidden). Existing groups get metadata before group creation so partial failures still update what is already local.

For private-key wallets, it imports missing EVM EOA keys in one KeyringController:withController pass (create simple keyring if needed), skips non-EOA entries for forward compatibility, and applies group metadata without renaming the keyring wallet.

Shared test helpers (makeLocalMnemonicWallet, payload builders, etc.) replace inline fixtures in export tests and back a large new import test suite. Messenger types gain WithController and createMultichainAccountWallet; the package build excludes test-only paths.

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[ccharly]

Adding the no-changelog since this change cannot be used until the main (integration) PR is merged.

Main PR changelog got updated here:

• 3bf247a

[gantunesr]

No major comments on my end. Will approve when the Bugbot comments and conflicts are resolved

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 3 total unresolved issues (including 2 from previous reviews).

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