Add support for numbers of arbitrary precision

[aSemy]

At the moment only Long and Double are supported. This means that numbers are not accurately encoded or decoded.

This limitation is due to a limitation of Kotlinx Serialization Kotlin/kotlinx.serialization#1405 Kotlin/kotlinx.serialization#1051

The Longs and Doubles could be converted to Java's BigDecimal and BigInteger. Alternatively, and planning for the future a bit more, use a multiplatform Kotlin implementation https://github.com/ionspin/kotlin-multiplatform-bignum.

Tasks

• Decide on an implementation
• Convert all Longs
• Convert all Doubles