feat(api): add #[non_exhaustive] to public types likely to evolve

ForwardingAction, TargetPattern, ForwardingRule, OperationType,
InterfaceConfig, InterfaceKind, DynamicConfig, and CallError are all
likely to gain variants/fields in future phases. Marking them
#[non_exhaustive] now prevents downstream breakage when new
variants/fields are added. Added constructor methods for types that
are constructed from other crates.

crates/alknet-core/src/call/spec.rs

@@ -2,6 +2,7 @@ use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[non_exhaustive]
 pub enum OperationType {
     Query,
     Mutation,