IMPORT: ebtree: switch the sizes and offsets to size_t and ssize_t

IMPORT: ebtree: switch the sizes and offsets to size_t and ssize_t

Let's use these in order to avoid 32-64 bit casts on 64 bit platforms.

This is cbtree commit e4f4c10fcb5719b626a1ed4f8e4e94d175468c34.
This is ebtree commit cc10507385c784d9a9e74ea9595493317d3da99e.