`--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.

Inizia dalla gestione della riga di comando di mypy per --enable-error-code e --warn-unreachable, usando il reproducer della issue come prima verifica. Confronta il comportamento di unreachable con quello di un codice non valido, quindi aggiungi o aggiorna test mirati da riga di comando in modo che l’abilitazione di unreachable funzioni senza --warn-unreachable, mentre i codici non validi continuino a essere rifiutati.