[Rust][DataFusion] Add Send + Sync to MemTable::load

[asfimport]

Add Send + Sync to the MemTable::load to allow the Spark persist behavior to be implemented for DataFrames

Reporter: Mike Seddon / @seddonm1
Assignee: Mike Seddon / @seddonm1

PRs and other links:

• GitHub Pull Request #9448

_{Note: This issue was originally created as ARROW-11561. Please see the migration documentation for further details.}

[asfimport]

Andrew Lamb / @alamb:
Issue resolved by pull request 9448
#9448