fix(linux): use #if os(macOS) instead of canImport for YYJSON

canImport(YYJSON) returns true on Linux because SwiftPM resolves
the module in the dependency graph, but Cyyjson C library isn't
linkable. Using os(macOS) provides deterministic compile-time check.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: alexey1312

Sources/ExFigCore/JSON/JSONCodec.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-#if canImport(YYJSON)
+#if os(macOS)
     import YYJSON
 #endif
 
@@ -14,7 +14,7 @@ public enum JSONCodec {
 
     /// Encode value to JSON data.
     public static func encode(_ value: some Encodable) throws -> Data {
-        #if canImport(YYJSON)
+        #if os(macOS)
             try YYJSONEncoder().encode(value)
         #else
             try JSONEncoder().encode(value)
@@ -23,7 +23,7 @@ public enum JSONCodec {
 
     /// Encode value to pretty-printed JSON.
     public static func encodePretty(_ value: some Encodable) throws -> Data {
-        #if canImport(YYJSON)
+        #if os(macOS)
             var encoder = YYJSONEncoder()
             encoder.writeOptions = [.prettyPrinted]
             return try encoder.encode(value)
@@ -38,7 +38,7 @@ public enum JSONCodec {
     ///
     /// Use for hashing where key order matters.
     public static func encodeSorted(_ value: some Encodable) throws -> Data {
-        #if canImport(YYJSON)
+        #if os(macOS)
             var encoder = YYJSONEncoder()
             encoder.writeOptions = [.sortedKeys]
             return try encoder.encode(value)
@@ -54,7 +54,7 @@ public enum JSONCodec {
     /// Use for Contents.json in xcassets where human-readable output
     /// with deterministic key order is needed.
     public static func encodePrettySorted(_ value: some Encodable) throws -> Data {
-        #if canImport(YYJSON)
+        #if os(macOS)
             var encoder = YYJSONEncoder()
             encoder.writeOptions = [.prettyPrintedTwoSpaces, .sortedKeys]
             return try encoder.encode(value)
@@ -67,7 +67,7 @@ public enum JSONCodec {
 
     /// Decode JSON data to type.
     public static func decode<T: Decodable>(_ type: T.Type, from data: Data) throws -> T {
-        #if canImport(YYJSON)
+        #if os(macOS)
             try YYJSONDecoder().decode(type, from: data)
         #else
             try JSONDecoder().decode(type, from: data)
@@ -76,7 +76,7 @@ public enum JSONCodec {
 
     /// Decode JSON data with ISO8601 date decoding strategy.
     public static func decodeWithISO8601Date<T: Decodable>(_ type: T.Type, from data: Data) throws -> T {
-        #if canImport(YYJSON)
+        #if os(macOS)
             var decoder = YYJSONDecoder()
             decoder.dateDecodingStrategy = .iso8601
             return try decoder.decode(type, from: data)
@@ -91,7 +91,7 @@ public enum JSONCodec {
     ///
     /// Use for checkpoint files where dates and human-readability matter.
     public static func encodeWithISO8601DatePretty(_ value: some Encodable) throws -> Data {
-        #if canImport(YYJSON)
+        #if os(macOS)
             var encoder = YYJSONEncoder()
             encoder.dateEncodingStrategy = .iso8601
             encoder.writeOptions = [.prettyPrinted]