chore(engine): re-add support for JRE 17

[qligier]

Fixes #510

[Copilot]

Pull request overview

This PR aims to restore Java 17 compatibility for matchbox-engine (and related modules) so the produced artifacts can be used on platforms limited to JRE 17 (per issue #510).

Changes:

• Removes the root POM’s Java 21 compiler release setting and compiler-plugin configuration.
• Sets Java compilation target to 17 in matchbox-engine and matchbox-server module POMs by adding maven-compiler-plugin configuration.
• Updates a matchbox-engine test to avoid Java 21’s List.getFirst() API.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
pom.xml	Removes the parent-level maven.compiler.release and parent compiler-plugin configuration.
matchbox-server/pom.xml	Sets module compilation target to Java 17 and adds compiler-plugin configuration.
matchbox-engine/pom.xml	Sets module compilation target to Java 17 and adds compiler-plugin configuration.
matchbox-engine/src/test/java/ch/ahdis/matchbox/engine/tests/CdaToFhirTransformTests.java	Replaces Java 21 List.getFirst() usage with Java 17-compatible indexing.

Comments suppressed due to low confidence (1)

pom.xml:44

• The compiler-plugin configuration (release/encoding/annotationProcessorPaths) is now duplicated across submodules. To keep Java target configuration consistent and avoid future modules accidentally compiling for the build JDK default, consider restoring a parent-level maven-compiler-plugin configuration and setting a default maven.compiler.release (likely 17) in the root pom.xml, letting submodules override only if necessary.

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

        <fhir.core.version>6.9.4</fhir.core.version>
        <hapi.fhir.version>8.8.0</hapi.fhir.version>

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