docs(tlv): update piece content metadata length

Signed-off-by: Gaius <gaius.qi@gmail.com>

Author: gaius-qi

src/tlv/piece_content.rs

@@ -50,24 +50,24 @@ const CREATED_AT_SIZE: usize = 8;
 /// PieceContent represents a piece metadata and piece content request.
 ///
 /// Value Format:
-/// - Metadata Length (8 bytes): Length of the metadata section.
+/// - Metadata Length (4 bytes): Length of the metadata section.
 /// - Number (4 bytes): Piece number to download.
 /// - Offset (8 bytes): Byte offset in the file.
 /// - Length (8 bytes): Length of the piece in bytes.
-/// - Digest Length (8 bytes): Length of the digest field (fixed at 32 bytes).
-/// - Digest (32 bytes): CRC32 hash of the piece content.
-/// - Parent ID Length (8 bytes): Length of the parent task identifier.
+/// - Digest Length (4 bytes): Length of the digest field.
+/// - Digest (variable): CRC32 hash of the piece content.
+/// - Parent ID Length (4 bytes): Length of the parent task identifier.
 /// - Parent ID (variable): Parent task identifier.
 /// - Traffic Type (1 byte): Network traffic classification type.
-/// - Cost (64 bytes): Download cost in seconds.
+/// - Cost (8 bytes): Download cost in seconds.
 /// - Created At (8 bytes): Creation timestamp as Unix epoch seconds.
 /// - Content (variable): Piece content bytes.
 ///
 /// ```text
 /// -------------------------------------------------------------------------------------------------------------------------------------
 /// | Metadata Length (4 bytes) | Number (4 bytes) | Offset (8 bytes) | Length (8 bytes) | Digest Length(8 bytes) | Digest (variable) |
 /// ------------------------------------------------------------------------------------------------------------------------------------------
-/// | Parent ID Length(8 bytes) | Parent ID (variable) | Traffic Type (1 byte) | Cost (8 bytes) | Created At (8 bytes) | Content (variable) |
+/// | Parent ID Length(4 bytes) | Parent ID (variable) | Traffic Type (1 byte) | Cost (8 bytes) | Created At (8 bytes) | Content (variable) |
 /// ------------------------------------------------------------------------------------------------------------------------------------------
 /// ```
 #[derive(Debug, Clone)]