refactor(keyring-snap-bridge)!: remove SnapKeyringV1 inheritance

[ccharly]

Removing inheritance so we the remaining v1 usage are explicit, since SnapKeyring (v2) was implicitly exposing v1 methods, it made it pretty difficult to sunset v1 completely.

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Note

High Risk
Breaking public API and behavior split across account creation, signing, and snap messages in security-sensitive keyring code; incorrect v1/v2 routing could break snaps or block v2-only accounts.

Overview
Breaking: v2 SnapKeyring no longer extends SnapKeyringV1. V1 behavior is exposed only via an optional .v1 getter (set when the snap manifest has no endowment:keyring capabilities; undefined for v2-only snaps).

The per-snap v2 class now owns its registry and v2 KeyringInternalSnapClient, and on deserialize may compose a SnapKeyringV1 that shares the same registry. createAccounts / submitRequest route to v1 or the v2 client depending on snap version (including the v1 { options } wrapper vs flat v2 options).

The top-level SnapKeyring coordinator routes legacy v1 entry points (messages, signing, user ops, etc.) through getKeyringV1For and throws clear errors when the target snap is v2-only. setSelectedAccounts uses keyring.v1?. so v2 snaps are skipped.

SnapKeyringV1 gains optional shared registry, public bindSnapId, and createAccounts for v1 RPC. Changelog and tests document the API shift and v1/v2 routing.

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[hmalik88]

Approving with the caveat that we don't merge until we test integration against the various preview builds we have up (sol, core, this)

[ccharly]

Was able to create account and the new .v1 is well defined when testing with the extension. Merging now so we can release and update core and the Solana Snap!