Fix few codegen errors to allow solidity compilation in Mock mode.

[0xalexbel]

Issue:

• Impl.sol does not compile in mock mode due to select function declared twice.

DeclarationError: Function with same name and parameter types defined twice.
   --> fhevm/mocks/Impl.sol:122:5:
    |
122 |     function select(uint256 control, uint256 ifTrue, uint256 ifFalse) internal pure returns (uint256 result) {
    |     ^ (Relevant source part starts here and spans across multiple lines).
Note: Other declaration is here:
   --> fhevm/mocks/Impl.sol:126:5:
    |
126 |     function select(uint256 control, uint256 ifTrue, uint256 ifFalse) internal pure returns (uint256 result) {
    |     ^ (Relevant source part starts here and spans across multiple lines).

• Impl.sol does not compile in mock mode due to implicit conversion error in verify function
• TFHE.sol does not compile in mock mode due to missing functions in Impl.sol

Solution:

• Remove the duplicate declaration in codegen/template.ts
• Change verify from einput to bytes32
• Add dummy ineffective missing functions in Impl.sol : allow + clearTranscientStorage

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[aquint-zama]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[immortal-tofu]

The mock has been fixed in the meantime.