Fix: Remove excluded modules from classpath

[dwijrajhari]

Problem (#141)

When a Maven module declares an <exclusion> on a transitive dependency, the excluded module's compiled output directory still appears on the Bloop classpath. This causes compilation failures in projects that use exclusions to manage classpath conflicts. This problem is reproducible in Spark (See #141 for details)

Solution

MavenProject.getArtifacts() returns the set of artifacts that survived Maven's full dependency resolution, including exclusion filtering. This PR uses this method as a gate before adding modules to the classpath.

Test plan

• Added integration test
• Validated the fix against Spark

$ mvn generate-sources ch.epfl.scala:bloop-maven-plugin:2.0.2-SNAPSHOT:bloopInstall
$ bloop compile spark-catalyst_2.13
Compiling spark-catalyst_2.13 (655 Scala sources and 237 Java sources)
...
...
Compiled spark-catalyst_2.13 (18776ms)

closes #141

cc: @tgodzik

[tgodzik]

LGTM!