build: cross-publish artifacts for Scala 2.13

[hongwei1]

Why

OBP-API is being migrated to Scala 2.13, and it consumes this repository through JitPack as com.github.OpenBankProject.lift-persistence:lift-persistence_${scala.version}. That artifact does not exist for 2.13:

lift-persistence_2.12-v1.0.4.pom -> HTTP 200
lift-persistence_2.12-v1.0.4.jar -> HTTP 200
lift-persistence_2.13-v1.0.4.pom -> HTTP 404
lift-persistence_2.13-v1.0.4.jar -> HTTP 404

The cause is visible in the JitPack build log for v1.0.4:

Running: sbt -Dsbt.log.noformat=true clean publishM2

JitPack's default sbt command has no +, so it publishes only the default Scala version. crossScalaVersions has always listed a 2.13 entry, but nothing ever published it. Tagging a new release without fixing this would still produce a 2.12-only artifact.

What

• Add jitpack.yml overriding the install command with +publishM2, so a single tag publishes both lift-persistence_2.12 and lift-persistence_2.13.
• Align the cross-build compiler versions with the ones OBP-API uses: 2.12.20 -> 2.12.21 and 2.13.16 -> 2.13.18, so the artifact and its consumer are built by the same compiler.

Verification

sbt +clean +compile +test on JDK 25, both versions, no source changes required:

Scala	main sources	test sources	Result
2.12.21	63	26	Passed: Total 406, Failed 0, Errors 0
2.13.18	63	26	Passed: Total 406, Failed 0, Errors 0

Zero [error] lines in the build log.

After this merges and a tag is cut, both artifacts must be verified by fetching the pom and jar directly — JitPack's maven-metadata.xml lists versions that do not exist and cannot be used as evidence.