revert-revert-erasure and erasure fixes (#3833)

* fix erasure, more tests for full blobs, more metrics

* Revert "Revert "Use Rust erasure library and turn on erasure (#3768)" (#3827)"

This reverts commit 4b8cb72977.

core/src/blocktree/kvs.rs

@@ -138,7 +138,6 @@ impl TypedColumn<Kvs> for cf::SlotMeta {
     type Type = super::SlotMeta;
 }
 
-#[cfg(feature = "erasure")]
 impl Column<Kvs> for cf::ErasureMeta {
     const NAME: &'static str = super::ERASURE_META_CF;
     type Index = (u64, u64);
@@ -157,7 +156,6 @@ impl Column<Kvs> for cf::ErasureMeta {
     }
 }
 
-#[cfg(feature = "erasure")]
 impl TypedColumn<Kvs> for cf::ErasureMeta {
     type Type = super::ErasureMeta;
 }