tempfile's Windows `persist` passes the raw paths to MoveFileExW and
SetFileAttributesW, bypassing std's extended-length handling. Once
`<object>/<rollback>/xl.meta.bkp` reached 260 UTF-16 units every delete
of that key failed with 500, while PUT and GET kept working.
Add `rustfs_utils::extended_length_path`, which normalizes a path with
GetFullPathNameW and prefixes it with `\\?\` (or `\\?\UNC\`), and use it
for the staging directory and destination handed to tempfile. Cover the
single and batch delete paths with a deep-key regression test and run the
helper's Windows assertions in the Windows filesystem workflow.
Fixes#8545
唐小鸭
62b6b6149c