Add support for kotlin multiplatform

[jmateoac]

This PR adds support for kotlin multiplatform.
I'm starting small by making Bech32Serde available since it was the easiest to decouple from the jvm.
I tested it on Android, Desktop (Mac M1), and iOS using a Compose Multiplatform app.

Todo

• Fix publishing so it uses info from the pom file
• Remove google maven repo

Issues I ran into and how I mitigated them

• Docker plugins don't work well with multiplatform, so I moved the tests to the lib-test module
• A vast majority of classes have dependencies on jvm frameworks. I moved them all to the jvmMain source set.
• I initially added an android target, but removed it because it introduced issues with secp256k1 libs.