perf(multichain-account-service): add v2 createAccounts (account batching when supported)

[ccharly]

Explanation

Implementing proper batching for our Solana account provider.

References

• perf(multichain-account-service): add :createMultichainAccountGroups action to batch account creation  #7801
• perf(account-tree-controller): use batched account creation in backup & sync #7907

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
Changes core Snap-based account creation to optionally use SnapKeyring.createAccounts for single and range derivations; misconfiguration or Snap incompatibilities could impact account creation or indexing across Sol/BTC/TRX.

Overview
Adds a config-gated v2 path for Snap-based providers to batch BIP-44 account creation via SnapKeyring.createAccounts, while keeping the existing per-account v1 flow as the default.

Refactors SnapAccountProvider to own createAccounts validation + timeout handling and introduces provider overrides (createAccountV1, optional toBip44Account) so SolAccountProvider, BtcAccountProvider, and TrxAccountProvider reuse shared batching logic; discovery now creates accounts through the shared helper.

Updates defaults to include createAccounts.v2: false, expands unit tests to cover v1 vs v2 behavior (single, range, idempotency, timeout), and adds small test utilities (DeepPartial, toGroupIndexRangeArray).

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