`abi.encodePacked` vs. `string.concat` (optimizer on, 200 runs, no via-ir) — bytecode of test files was also identical

output.txt

$ forge test -vvv
[⠢] Compiling...
[⠒] Compiling 1 files with 0.8.19
[⠆] Solc 0.8.19 finished in 887.23ms
Compiler run successful!

Running 1 test for test/Counter.t.sol:TestShort_EncodePacked
[PASS] test1() (gas: 4373)
Logs:
  462
  helloworld

Test result: ok. 1 passed; 0 failed; finished in 328.75µs

Running 1 test for test/Counter.t.sol:TestShort_StringConcat
[PASS] test1() (gas: 4373)
Logs:
  462
  helloworld

Test result: ok. 1 passed; 0 failed; finished in 328.71µs

Running 1 test for test/Counter.t.sol:TestLong_StringConcat
[PASS] test1() (gas: 5032)
Logs:
  745
  hello hello hello hello hello hello hello hello hello hello hello hello hello hello helloworld world world world world world world world world world world world world world world

Test result: ok. 1 passed; 0 failed; finished in 277.92µs

Running 1 test for test/Counter.t.sol:TestLong_EncodePacked
[PASS] test1() (gas: 5032)
Logs:
  745
  hello hello hello hello hello hello hello hello hello hello hello hello hello hello helloworld world world world world world world world world world world world world world world

Test result: ok. 1 passed; 0 failed; finished in 339.21µs

strings.t.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.19;

import "forge-std/Test.sol";

contract TestShort_EncodePacked is Test {
    function test1() public view {
        string memory x = "hello";
        string memory y = "world";
        uint256 startGas = gasleft();
        string memory z = string(abi.encodePacked(x, y));
        console2.log(startGas - gasleft());
        console2.log(z);
    }
}

contract TestShort_StringConcat is Test {
    function test1() public view {
        string memory x = "hello";
        string memory y = "world";
        uint256 startGas = gasleft();
        string memory z = string.concat(x, y);
        console2.log(startGas - gasleft());
        console2.log(z);
    }
}

contract TestLong_EncodePacked is Test {
    function test1() public view {
        string memory x = "hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello";
        string memory y = "world world world world world world world world world world world world world world world";
        uint256 startGas = gasleft();
        string memory z = string(abi.encodePacked(x, y));
        console2.log(startGas - gasleft());
        console2.log(z);
    }
}

contract TestLong_StringConcat is Test {
    function test1() public view {
        string memory x = "hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello";
        string memory y = "world world world world world world world world world world world world world world world";
        uint256 startGas = gasleft();
        string memory z = string.concat(x, y);
        console2.log(startGas - gasleft());
        console2.log(z);
    }
}