Fix pwd.getpwuid raising OSError for unknown uids (#9106)

When a uid does not exist, some NSS backends (systemd-userdb, sssd,
LDAP) make getpwuid_r() return a non-zero errno such as ENOENT. POSIX
expects success with a NULL result instead. That errno was surfacing as
FileNotFoundError and broke test_pwd.test_errors.

Match CPython's pwdmodule.c: raise MemoryError only for ENOMEM, and
treat any other failure as "not found" (KeyError).

Assisted-by: Antigravity:Claude Opus 5.5

crates/vm/src/stdlib/pwd.rs

@@ -5,8 +5,8 @@ pub(crate) use pwd::module_def;
 #[pymodule]
 mod pwd {
     use crate::{
-        PyResult, VirtualMachine, builtins::PyUtf8StrRef, convert::IntoPyException, exceptions,
-        function::ArgIndex, types::PyStructSequence,
+        PyResult, VirtualMachine, builtins::PyUtf8StrRef, exceptions, function::ArgIndex,
+        types::PyStructSequence,
     };
     use core::hint::cold_path;
     use rustpython_host_env::pwd as host_pwd;
@@ -67,12 +67,16 @@ mod pwd {
     #[pyfunction]
     fn getpwuid(uidobj: ArgIndex, vm: &VirtualMachine) -> PyResult<PasswdData> {
         let uidobj = uidobj.into_int_ref();
-        let uid_t = libc::uid_t::try_from(uidobj.as_bigint()).ok();
-        let user = uid_t
+        let user = match libc::uid_t::try_from(uidobj.as_bigint())
+            .ok()
             .map(host_pwd::getpwuid)
-            .transpose()
-            .map_err(|err| err.into_pyexception(vm))?
-            .flatten();
+        {
+            Some(Ok(user)) => user,
+            Some(Err(err)) if err.raw_os_error() == Some(libc::ENOMEM) => {
+                return Err(vm.no_memory_error());
+            }
+            _ => None,
+        };
         let user = user.ok_or_else(|| {
             vm.new_key_error(
                 vm.ctx