* fix(ecstore): remove dead _buf field from Erasure struct
_buf was allocated in new(), clone(), and Default but never read or written.
Each clone() was allocating block_size bytes (typically 10MB) for nothing.
- Remove _buf from struct, Default, Clone, new_with_options
- 51 erasure tests pass
* fix: remove empty line after doc comment
---------
Co-authored-by: houseme <[email protected]>