`--enable-error-code code` does not enable some error codes, yet neither are they reported as an invalid error codes

In my understanding, --enable-error-code unreachable should have the same effect as --warn-unreachable. But, instead, it seems to have no effect, and doesn't even produce an error.

$uvx mypy -c "if False: print('hello')"
Success: no issues found in 1 source file

$uvx mypy -c "if False: print('hello')" --warn-unreachable
<string>:1: error: Statement is unreachable  [unreachable]
Found 1 error in 1 file (checked 1 source file)

$uvx mypy -c "if False: print('hello')" --enable-error-code unreachable
Success: no issues found in 1 source file

$uvx mypy -c "if False: print('hello')" --enable-error-code unreachable --warn-unreachable
<string>:1: error: Statement is unreachable  [unreachable]
Found 1 error in 1 file (checked 1 source file)

$uvx mypy -c "if False: print('hello')" --enable-error-code funnyerrorcodenotreal
usage: mypy [-h] [-v] [-V] [more options; see below]
            [-m MODULE] [-p PACKAGE] [-c PROGRAM_TEXT] [files ...]
mypy: error: Invalid error code(s): funnyerrorcodenotreal

Based on my testing, this seems to have been the case since 1.0.0 and maybe before, and thus is not a recent regression.

まず、--enable-error-code と --warn-unreachable に対する mypy のコマンドライン処理から始め、issue の reproducer を最初の確認に使います。unreachable と無効なコードの挙動を比較し、その後、無効なコードは引き続き拒否される一方で、--warn-unreachable なしで unreachable を有効にできるよう、焦点を絞ったコマンドラインテストを追加または更新します。