🧹 chore: drop support for Scala 2.12 (#689)

[gaeljw]

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Fixes

Closes #689

Additional details

As part of this, the module anorm-iteratee is removed as it was only published for Scala 2.12.

[Copilot]

Pull request overview

This PR drops Scala 2.12 from the build matrix and removes the Scala-2.12-only iteratee module, simplifying cross-build configuration around Scala 2.13 and Scala 3.

Changes:

• Updates default/cross Scala versions and CI Scala matrices to 2.13/3 only.
• Removes the anorm-iteratee project, source, tests, and manual section.
• Moves compatibility helpers into common source locations now that Scala 2.12-specific variants are no longer needed.

Reviewed changes

Copilot reviewed 8 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
project/Common.scala	Removes Scala 2.12 cross-build settings and compatibility source directory routing.
build.sbt	Removes iteratee project wiring and simplifies Akka/Pekko/docs settings for supported Scala versions.
.github/workflows/build-test.yml	Updates CI Scala matrices from 2.12 to 2.13/3.
core/src/main/scala/anorm/Compat.scala	Adds unified Scala 2.13+/3 compatibility helpers.
core/src/main/scala-2.13-/Compat.scala	Removes old Scala 2.12 compatibility implementation.
akka/src/test/scala/anorm/AkkaCompat.scala	Adds unified Akka test compatibility alias.
akka/src/test/scala-2.13-/AkkaCompat.scala	Removes old Scala 2.12 Akka compatibility alias.
pekko/src/test/scala/anorm/PekkoCompat.scala	Adds unified Pekko test compatibility alias.
pekko/src/test/scala-2.13-/PekkoCompat.scala	Removes old Scala 2.12 Pekko compatibility alias.
iteratee/src/main/scala/anorm/Iteratees.scala	Deletes iteratee integration implementation.
iteratee/src/test/scala/anorm/IterateeSpec.scala	Deletes iteratee integration tests.
docs/manual/working/scalaGuide/main/sql/ScalaAnorm.md	Removes the iteratee documentation section from the main manual.

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[gaeljw]

ℹ️ I removed it because the combo Java 8 and Scala 2.13 doesn't work

Exception in thread "specs2-3" java.lang.BootstrapMethodError: java.lang.UnsupportedClassVersionError: play/api/test/WithApplication has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

This because our setup for Scala 2.13 pulls Play 3.x which requires Java 11+.

As we're gonna baseline on Java 17 soon ( #708 ), I don't feel it's worth making it work by changing the Play version targeted.

Actually I'm not even sure what was the purpose of this double pipeline in Java 8 & 11 but not testing all Scala version for Java 8. Anyway, as I said, we're dropping Java 8.