authfs: refine/rename trait ReadOnlyDataByChunk

 - ReadOnlyDataByChunk is renamed to ReadByChunk
 - `fn read_chunk` now takes a fixed-size array of chunk size
 - Behavior change:
   1. Reading beyond file size now should not crash, and should return 0.
   2. `read_chunk` should return a full chunk unless it's the last
      (wasn't clearly defined previously).

Bug: 181674212
Bug: 182173887
Test: atest

Change-Id: I7017b5ed986d0bfc594da58a1ed9f59ac555643e
diff --git a/authfs/src/fusefs.rs b/authfs/src/fusefs.rs
index 13ec87d..4728418 100644
--- a/authfs/src/fusefs.rs
+++ b/authfs/src/fusefs.rs
@@ -34,7 +34,7 @@
 
 use crate::common::{divide_roundup, ChunkedSizeIter, CHUNK_SIZE};
 use crate::file::{
-    LocalFileReader, RandomWrite, ReadOnlyDataByChunk, RemoteFileEditor, RemoteFileReader,
+    LocalFileReader, RandomWrite, ReadByChunk, RemoteFileEditor, RemoteFileReader,
     RemoteMerkleTreeReader,
 };
 use crate::fsverity::{VerifiedFileEditor, VerifiedFileReader};
@@ -123,7 +123,7 @@
     offset / CHUNK_SIZE
 }
 
-fn read_chunks<W: io::Write, T: ReadOnlyDataByChunk>(
+fn read_chunks<W: io::Write, T: ReadByChunk>(
     mut w: W,
     file: &T,
     file_size: u64,