feat(tempo): support v2 keychain signature type

[jxom]

Summary

Adds support for V2 keychain signatures following the tempoxyz/tempo PR #2867 specification.

Changes

• New signature type byte 0x04 for V2 keychain signatures (V1 remains 0x03)
• KeychainVersion type ('v1' | 'v2') and version field on Keychain / KeychainRpc types, defaulting to 'v2'
• SignatureEnvelope.serialize / deserialize handle both 0x03 (V1) and 0x04 (V2) type bytes
• TxEnvelopeTempo.getSignPayload accepts a from option for V2 keychain signing, computing keccak256(sigHash || from) to bind the signature to the user account

Breaking Changes

1. KeyAuthorization.chainId is now required (previously optional, defaulted to 0n)
2. Keychain signatures default to V2 (0x04). To use legacy V1 format, set version: 'v1'

See .changeset/v2-keychain-auth.md for migration examples.

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Project	Deployment	Actions	Updated (UTC)
ox	Ready	Preview, Comment	Feb 27, 2026 2:48am

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