Migrate simple-store to kotlin and coroutines

[tyvsmith]

Before pressing the "Create Pull Request" button, please provide the following:

  - [x] A description about what and why you are contributing, even if it's trivial.
This PR migrates the `simplestore` module from Java to Kotlin, replacing `ListenableFuture` with Kotlin coroutines for asynchronous operations. It includes adding coroutines dependencies, converting all Java source files in the module to Kotlin, and providing `ListenableFuture` extension functions to maintain API compatibility for Java callers. Additionally, Gradle and plugin versions were updated to resolve Java 21 compatibility issues.

  - [ ] The issue number(s) or PR number(s) in the description if you are contributing in response to those.
N/A

  - [ ] If applicable, unit tests.
Existing unit tests were run to verify the migration. Test source code migration will follow in a subsequent PR.