This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.

This change uses the Java Platform functionality from Gradle to enable
shared dependency constraints across modules.

This change updates the Gradle configuration to utilize version
constraints to force the same dependency version across modules.

This change moves the version of the dependencies from buildSrc to
gradle.properties to prevent recompilation when changing dependency
versions.

This change extracts the configuration for test from the Kotlin library
conventions.

This change removes unnecessary dependencies on JUnit Platform launcher
from the repository. Previously, the launcher was used to bootstrap
tests for Gradle when it did not natively support JUnit Platform.

Gradle now has native support for JUnit Platform, so the dependency is
not needed anymore.

This change converts the low-level workload model to be pull-based. This
reduces the overhead that we experienced with our previous co-routine
based approach.

This change moves the OpenDC modules previously living in the simulator/opendc
directory to the simulator directory itself given that we do not make a
distinction between OpenDC and odcsim anymore.