[Rust] Improve performance of MutableBuffer

[asfimport]

Reporter: Jorge Leitão / @jorgecarleitao
Assignee: Jorge Leitão / @jorgecarleitao

PRs and other links:

• GitHub Pull Request #9076

_{Note: This issue was originally created as ARROW-11108. Please see the migration documentation for further details.}

[asfimport]

Jorge Leitão / @jorgecarleitao:
Issue resolved by pull request 9076
#9076