Set up explicit Mockito instrumentation

[GuusLieben]

Type of Change

• Chore (changes to the build process or auxiliary tools)

Description

For a while now we've received the warning below regarding Mockito dynamically attaching its agent:

Mockito is currently self-attaching to enable the inline-mock-maker. This will no longer work in future releases of the JDK. Please add Mockito as an agent to your build as described in Mockito's documentation: https://javadoc.io/doc/org.mockito/mockito-core/latest/org.mockito/org/mockito/Mockito.html#0.3
WARNING: A Java agent has been loaded dynamically (/Users/guuslieben/.m2/repository/net/bytebuddy/byte-buddy-agent/1.17.7/byte-buddy-agent-1.17.7.jar)
WARNING: If a serviceability tool is in use, please run with -XX:+EnableDynamicAgentLoading to hide this warning
WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
WARNING: Dynamic loading of agents will be disallowed by default in a future release

With the recent upgrade to Java 25, we're long overdue to address this warning properly. As such, this PR explicitly sets up the Mockito agent.

Checklist

• I have performed a self-review of my own code
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have rebased my branch on top of the latest develop branch