72 cea tx type funds and payload

[zaryab2000]

this fixes #72

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v2 review fixes

• sendUniversalTxToUEA: Removed payload.length == 0 branching — all calls (FUNDS and
  FUNDS_AND_PAYLOAD) now route through sendUniversalTxViaCEA unconditionally
• _handleExecution: Replaced two-path routing (multicall vs single-call with inline migration
  detection) with a clean three-way branch: isMulticall → _handleMulticall, isMigrationPayload →
  _handleMigration, else → _handleSingleCall
• _handleMulticall: Removed totalValue accumulation loop and msg.value != totalValue revert (CEA
  can now spend pre-existing balance alongside Vault-provided msg.value). Added
  isMigration(calls[i].data) guard that reverts InvalidCall to prevent migration selector inside
  multicall arrays
• _handleMigration: Simplified from _handleMigration(Multicall memory call) to _handleMigration()
  — no params, no target/value validation. Fetches migration contract from factory and
  delegatecalls directly. Migration is now a top-level payload, not wrapped in a Multicall struct
• Added isMigrationPayload(bytes calldata): New private helper (calldata variant) for top-level
  migration detection in _handleExecution's three-way branch, alongside the existing
  isMigration(bytes memory) used for in-loop multicall checking
• Fixed unused variable warning: Changed (bool success, bytes memory returnData) to (bool
  success,) in _handleMulticall