[authfs][refactoring] Use crate hex to decode hex string

Bug: 239413416
Test: m authfs && atest authfs_device_test_src_lib
Change-Id: I9379ed34c577e8f8ca365186470a298740b43c2c
diff --git a/authfs/Android.bp b/authfs/Android.bp
index a4151c2..8ac600d 100644
--- a/authfs/Android.bp
+++ b/authfs/Android.bp
@@ -19,6 +19,7 @@
         "libclap",
         "libfsverity_digests_proto_rust",
         "libfuse_rust",
+        "libhex",
         "liblibc",
         "liblog_rust",
         "libnix",