typing: add stub functions for `cext/charencoding`

I'm not sure if it's better to have a separate file, and currently pytype
doesn't really know how to handle these, so it's no help in figuring that out.
Technically, these methods are part of the `mercurial.cext.parsers` module, so
put them into the existing stub until there's a reason to split it out.

mercurial/cext/parsers.pyi

@@ -1,82 +1,97
 from typing import (
     Callable,
     Dict,
     Iterator,
     List,
     Optional,
     Set,
     Tuple,
     Union,
 )
 
 version: int
 versionerrortext: str
 
+# From charencode.c
+
+# Note: the first 'bytes' arg of isasciistr() can be typed as 'Buffer' from the
+# typing_extensions backport, once the related bug is fixed in pytype, or pytype
+# is run under py3.12.  The arg for asciilower(), asciiupper() and
+# jsonescapeu8fast() is checked specifically for the 'bytes' type.  The 'bytes'
+# return is an instance of 'bytes', not an alias for 'Buffer'.
+#
+# https://github.com/google/pytype/issues/1772
+def isasciistr(s: bytes) -> bool: ...
+def asciilower(s: bytes) -> bytes: ...
+def asciiupper(s: bytes) -> bytes: ...
+def jsonescapeu8fast(u8chars: bytes, paranoid: bool) -> bytes: ...
+
+
 class DirstateItem:
     __doc__: str
 
     def __len__(self) -> int: ...
     def __getitem__(self, key: int) -> Union[bytes, int]: ...
 
 # From dirs.c
 
 class dirs:
     __doc__: str
     def __init__(self, source, skipchar: bytes): ...
     def __iter__(self) -> Iterator[bytes]: ...
     def addpath(self, path: bytes) -> None: ...
     def delpath(self, path: bytes) -> None: ...
 
 # From manifest.c
 class lazymanifest:
     def __init__(self, nodelen: int, data: bytes): ...
     def __iter__(self) -> Iterator[bytes]: ...
 
     def __len__(self) -> int: ...
     def __getitem__(self, item: bytes) -> Optional[Tuple[bytes, bytes]]: ...
     def __setitem__(self, key: bytes, value: Tuple[bytes, bytes]) -> None: ...
     def __delitem__(self, key: bytes) -> None: ...
 
     def iterkeys(self) -> Iterator[bytes]: ...
     def iterentries(self) -> Iterator[Tuple[bytes, bytes, bytes]]: ...
     def copy(self) -> lazymanifest: ...
     def filtercopy(self, matchfn: Callable[[bytes], bool]) -> lazymanifest: ...
     def diff(self, other: lazymanifest, clean: Optional[bool]) -> Dict[bytes, Tuple[bytes, Tuple]]: ...
     def text(self) -> bytes: ...
 
 # From revlog.c
 
 class index:
     __doc__: str
 
     nodemap: Dict[bytes, int]
 
     def ancestors(self, *args: int) -> Iterator[int]: ...
     def commonancestorsheads(self, *args: int) -> List[int]: ...
     def clearcaches(self) -> None: ...
     def get(self, value: bytes) -> Optional[int]: ...
     def get_rev(self, value: bytes) -> Optional[int]: ...
     def has_node(self, value: Union[int, bytes]) -> bool: ...
     def rev(self, node: bytes) -> int: ...
     def computephasesmapsets(self, root: Dict[int, Set[int]]) -> Tuple[int, Dict[int, Set[bytes]]]: ...
     def reachableroots2(self, minroot: int, heads: List[int], roots: List[int], includepath: bool) -> List[int]: ...
     def headrevs(self, filteredrevs: Optional[List[int]]) -> List[int]: ...
     def headrevsfiltered(self, filteredrevs: Optional[List[int]]) -> List[int]: ...
     def issnapshot(self, value: int) -> bool: ...
     def findsnapshots(self, cache: Dict[int, List[int]], start_rev: int) -> None: ...
     def deltachain(self, rev: int, stop: int, generaldelta: bool) -> Tuple[List[int], bool]: ...
     def slicechunktodensity(self, revs: List[int], targetdensity: float, mingapsize: int) -> List[List[int]]: ...
     def append(self, value: Tuple[int, int, int, int, int, int, int, bytes]) -> None: ...
     def partialmatch(self, node: bytes) -> bytes: ...
     def shortest(self, value: bytes) -> int: ...
     def stats(self) -> Dict[bytes, int]: ...
 
 class nodetree:
     __doc__: str
 
     def insert(self, rev: int) -> None: ...
     def shortest(self, node: bytes) -> int: ...
 
 # The IndexObject type here is defined in C, and there's no type for a buffer
 # return, as of py3.11.  https://github.com/python/typing/issues/593
 def parse_index2(data: object, inline: object, format: int = ...) -> Tuple[object, Optional[Tuple[int, object]]]: ...