contrib/clang-format-ignorelist

rust-status: query fs traversal metadata lazily

Currently, any time the status algorithm needs to read a directory from the
filesystem (because the stat-only optimization is not available), it also
stats each directory entry eagerly.

Stat'ing the entries is only needed in a few cases (like when checking
the mtime of a directory for caching): this patch creates a wrapper struct
`DirEntry` that only stats the directory entry it represents when needed.

Excerpt of an `strace` before this change on Mozilla Central:

```
openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
newfstatat(3, "", {st_mode=S_IFDIR|0755, st_size=3540, ...}, AT_EMPTY_PATH) = 0
getdents64(3, 0x55dc970bd440 /* 139 entries */, 32768) = 5072
statx(3, ".hg", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0755, stx_size=772, ...}) = 0

[... 135 other successful `statx` calls]

getdents64(3, 0x55dc970bd440 /* 0 entries */, 32768) = 0
close(3)                                = 0
```

After this change:

```
openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
newfstatat(3, "", {st_mode=S_IFDIR|0755, st_size=3540, ...}, AT_EMPTY_PATH) = 0
getdents64(3, 0x561567c10190 /* 139 entries */, 32768) = 5072
getdents64(3, 0x561567c10190 /* 0 entries */, 32768) = 0
close(3)                                = 0
```

# Files that just need to be migrated to the formatter.
# Do not add new files here!
mercurial/cext/manifest.c
mercurial/cext/osutil.c
# Vendored code that we should never format:
syntax: glob
contrib/python-zstandard/**.c
contrib/python-zstandard/**.h
hgext/fsmonitor/pywatchman/**.c
mercurial/thirdparty/**.c
mercurial/thirdparty/**.h
mercurial/pythoncapi_compat.h