Implement session call digest for v3 sessions

[Agusx1211]

This implements the digest that a session key has to sign for each call of a v3 payload, needed for waas smart-sessions (7193). The old hashCallWithReplayProtection was a leftover stub, unexported and with no callers, so I replaced it with an exported HashCallWithReplayProtection that matches SessionSig.hashPayloadCallIdx in wallet-contracts-v3: keccak256(Payload.hashFor(payload, wallet) ++ uint256(callIdx)).

Note that the digest scheme the stub hinted at (chainId ++ space ++ nonce ++ callHash) is no longer what the contracts verify, it was removed in the audit fix for partial payload replay (0xsequence/wallet-contracts-v3#89), so implementing it as described would produce signatures that never pass on-chain.

The test vectors in session_digest_test.go were generated from SessionSig.hashPayloadCallIdx itself, with a forge test constructing identical payloads, so the test asserts parity with the on-chain verification. I also checked that a signature produced over this digest recovers to the right signer through plain ecrecover, which is the exact path the contract uses (no EIP-191 prefix).