* fix(s3): return ETag header for directory marker PutObject requests
The PutObject handler has a special path for keys ending with "/" (directory
markers) that creates the entry via mkdir. This path never computed or set
the ETag response header, unlike the regular PutObject path. AWS S3 always
returns an ETag header, even for empty-body puts.
Compute the MD5 of the content (empty or otherwise), store it in the entry
attributes and extended attributes, and set the ETag response header.
Fixes#8682
* fix: handle io.ReadAll error and chunked encoding for directory markers
Address review feedback:
- Handle error from io.ReadAll instead of silently discarding it
- Change condition from ContentLength > 0 to ContentLength != 0 to
correctly handle chunked transfer encoding (ContentLength == -1)
* fix hanging tests
c197206897