feat(me): add EdDSA MPCv2 key generation callback factory

[Marzooqa]

What

• Add createEddsaMPCv2KeyGenCallbacks(awmUserClient, awmBackupClient) to src/masterBitgoExpress/handlers/walletGenerationCallbacks.ts, returning the SDK's EddsaMPCv2KeyGenCallbacks four-callback contract:
  • initializeCallback — both AWMs generate GPG pairs; returns pubs + packed state
  • round1Callback — both AWMs run DKG round 1; returns signed msg1s + updated state
  • round2Callback — both AWMs run DKG round 2; returns signed msg2s + updated state
  • finalizeCallback — both AWMs finalize; asserts commonKeychain match; returns { commonKeychain }

Design notes

• Finalize bridge: the SDK's finalizeCallback params do not include userSignedMsg2/backupSignedMsg2, but the user's finalize needs the backup's signed msg2 (and vice versa) — they are carried in the factory closure (same pattern as the ECDSA factory's inter-party messages)
• State packing: per-party keygen state (encrypted data key, encrypted GPG prv, round-1/round-2 sessions, GPG pub keys) is threaded through the SDK's ExternalSignerMpcState as a JSON blob in encryptedData
• Four-callback contract (not the incompatible three-callback variant on the stale WCI-895-pt1/pt2 branches, which collapsed SDK round 1 into initialize and SDK round 2 into round1)

Why

• WCI-895 of the WCI-888 plan: the SDK orchestrator (EddsaMPCv2Utils.createKeychainsWithExternalSigner) drives the callbacks; this factory wires them to the AWM via the WCI-893 client method

Dependencies

• Stacked on the WCI-893 PR (the client method this factory calls)

Test plan

• tsc --noEmit clean; ESLint clean
• Exercised end-to-end by WCI-918 routing tests and the WCI-896 E2E (follow-up)

Ticket: WCI-895

[linear-code]

WCI-895