internal/subprocess(refactor[typing]): Tighten subprocess param types

why: Reduce use of overly broad types for SubprocessCommand parameters.
what:
- Narrow _FILE to IO[str] | IO[bytes]
- Specify preexec_fn returns None
- Constrain pass_fds to sequence of ints

Author: tony

src/libvcs/_internal/subprocess.py

@@ -63,7 +63,7 @@ def __init__(self, output: str, *args: object) -> None:
     _ENV: t.TypeAlias = Mapping[str, str]
 else:
     _ENV: t.TypeAlias = Mapping[bytes, StrOrBytesPath] | Mapping[str, StrOrBytesPath]
-_FILE: t.TypeAlias = None | int | t.IO[t.Any]
+_FILE: t.TypeAlias = None | int | t.IO[str] | t.IO[bytes]
 _TXT: t.TypeAlias = bytes | str
 #: Command
 _CMD: t.TypeAlias = StrOrBytesPath | Sequence[StrOrBytesPath]
@@ -96,7 +96,7 @@ class SubprocessCommand(SkipDefaultFieldsReprMixin):
     stdin: _FILE = None
     stdout: _FILE = None
     stderr: _FILE = None
-    preexec_fn: t.Callable[[], t.Any] | None = None
+    preexec_fn: t.Callable[[], None] | None = None
     close_fds: bool = True
     shell: bool = False
     cwd: StrOrBytesPath | None = None
@@ -109,7 +109,7 @@ class SubprocessCommand(SkipDefaultFieldsReprMixin):
     # POSIX-only
     restore_signals: bool = True
     start_new_session: bool = False
-    pass_fds: t.Any = ()
+    pass_fds: Sequence[int] = ()
     umask: int = -1
     pipesize: int = -1
     user: str | None = None