Replace copy constructor with a copy method for all CRDTs

src/commonMain/kotlin/crdtlib/crdt/BCounter.kt

src/commonMain/kotlin/crdtlib/crdt/DeltaCRDT.kt

src/commonMain/kotlin/crdtlib/crdt/LWWMap.kt

src/commonMain/kotlin/crdtlib/crdt/LWWRegister.kt

src/commonMain/kotlin/crdtlib/crdt/MVMap.kt

src/commonMain/kotlin/crdtlib/crdt/MVRegister.kt

src/commonMain/kotlin/crdtlib/crdt/Map.kt

src/commonMain/kotlin/crdtlib/crdt/PNCounter.kt

src/commonMain/kotlin/crdtlib/crdt/RGA.kt

src/commonMain/kotlin/crdtlib/crdt/Ratchet.kt

src/commonTest/kotlin/crdtlib/crdt/MVRegisterPropTest.kt

src/commonTest/kotlin/crdtlib/crdt/MVRegisterTest.kt