rgw_cksum: address review comments

rgw_cksum: address review comments

* remove rgw_cksum_pipe state enum, not needed [Casey review]
* remove a format that just took a single string substitution
  and passed it to an iostream [Casey review]
* use boost::to_upper* [Casey review]
* remove unused RGW_ATTR_CKSUM_ALGORITHM decl [Casey review]
* negate error code values in two places [Casey review]
* split cksum digests from base type decls
* resolve comment when checksum requested but not available
* remove redundant memset
* remove junk from rgw_blake3_digest.h
* s/ldpp_dout + fmt::format/ldpp_dout_fmt/g;
* fix conditional return of parts_count
      from RGWRados::Object::prepare().  A value for parts_count should
      be returned iff a *multipart* object manifest exists.
* remove /tmp output test
* finish moving ceph_crypto headers out of rgw_cksum.h
* consume the optional in multipart_parts_count
* target_attrs can be a reference (but not const)

Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>