feat: add optional createAccounts method based on KeyringV2

[ccharly]

Adding a new optional createAccounts method that we could already leverage today without having the full implementation of KeyringV2.

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Note

Medium Risk
Adds a new account-creation RPC path and Snap bridge state updates, which could affect account provisioning and persistence if responses are malformed or validation differs across clients. The change is mostly additive/optional but touches core account-management surfaces (Keyring, RPC handler, Snap bridge/client).

Overview
Adds an optional Keyring.createAccounts(options: CreateAccountOptions) for batch account creation (KeyringV2-typed options) and introduces the keyring_createAccounts RPC method with request/response validation structs.

Implements batch creation in SnapKeyring.createAccounts, calling through to the internal snap client, inserting returned accounts into the bridge’s internal map, validating generic AnyAccountType.Account when disallowed, and persisting state once (no per-account notify:accountCreated/addAccount callback).

Extends KeyringClient to send keyring_createAccounts and updates keyring-snap-sdk request dispatch to route/guard the new method (throws MethodNotSupportedError if unimplemented), with comprehensive new tests and changelog entries across packages.

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

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Partial failure leaves accounts in inconsistent state

Medium Severity

In createAccounts, if validation fails partway through the loop (e.g., account N is a generic AnyAccountType.Account when not allowed), accounts 0 through N-1 have already been added to this.#accounts in memory but saveState() is never called. Additionally, the Snap has already created all accounts via client.createAccounts() before validation. This leaves the system in an inconsistent state: some accounts exist in the bridge's memory (but unpersisted), while the Snap has created all accounts. On restart, the in-memory accounts would be lost but still exist on the Snap side.