Concurrent with_entries mismatches sequential implementation due to unsorted keys in multiple-entry leaves

[krushimir]

The concurrent implementation of with_entries fails to correctly construct leaves when multiple entries are stored in a single leaf and keys are not sorted before constructing the leaf.

This causes inconsistencies between the sequential and concurrent implementations.

The issue arises due to a behavior discrepancy between SmtLeaf::insert and SmtLeaf::new_multiple. Note that SmtLeaf::new_multiple doesn't mention sorted input as requirement.

Will be addressed in #385