Fix is_multiple_of nightly API, bump to 0.8.3

Replace s.len().is_multiple_of(2) with s.len() % 2 != 0 for stable Rust.
This was fixed previously but regressed.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "libfreemkv"
-version = "0.8.2"
+version = "0.8.3"
 edition = "2021"
 license = "AGPL-3.0-only"
 description = "Open source raw disc access library for optical drives"

src/aacs/keydb.rs

@@ -57,7 +57,7 @@ pub struct DiscEntry {
 /// Parse a hex string like "0xABCD..." into bytes.
 pub(crate) fn parse_hex(s: &str) -> Option<Vec<u8>> {
     let s = s.trim().trim_start_matches("0x").trim_start_matches("0X");
-    if !s.len().is_multiple_of(2) {
+    if s.len() % 2 != 0 {
         return None;
     }
     let mut out = Vec::with_capacity(s.len() / 2);