authfs: implement fs-verity Merkle tree verification

The fs-verity verification is compatible to the original format in Linux
kernel. The current verification only verifies a chunk of content
against the Merkle tree, without any signature check yet.

Bug: 171310075
Test: atest authfs_host_test_src_lib
Test: stress test with lots of possible input sizes

Change-Id: Icf2194aa5ebf282936d7b304bcc956d39f500b1a
diff --git a/authfs/src/lib.rs b/authfs/src/lib.rs
index c128f62..26de157 100644
--- a/authfs/src/lib.rs
+++ b/authfs/src/lib.rs
@@ -23,4 +23,5 @@
 //! The implementation is not finished.
 
 mod crypto;
+mod fsverity;
 mod reader;