fix: enforce ifd_value_size limits and detect PackBits under-decode

Two input validation fixes:

- vec_with_capacity now checks raw IFD value bytes against
  ifd_value_size before allocating. Previously only the in-memory
  Value representation was bounded (by decoding_buffer_size), so a
  crafted IFD with a large count of small-typed values could allocate
  based on raw byte count without limit checking. Also fix ASCII value
  parsing to check ifd_value_size instead of decoding_buffer_size.

- LogLuv PackBits decoder now verifies that the expected number of
  pixels was actually decoded per plane, returning UnexpectedEof if
  the RLE stream ends short.

src/decoder/logluv.rs

@@ -87,6 +87,7 @@ fn packbits_decode<R: Read, const N: usize>(
     reader: &mut R,
     buf: &mut [[u8; N]],
 ) -> std::io::Result<()> {
+    let expected = buf.len();
     for offset in (0..N).rev() {
         let mut i = 0;
         let mut code = [0u8; 1];
@@ -124,6 +125,13 @@ fn packbits_decode<R: Read, const N: usize>(
                 i += usize::from(repeat);
             }
         }
+
+        if i < expected {
+            return Err(std::io::Error::new(
+                std::io::ErrorKind::UnexpectedEof,
+                "PackBits RLE decoded fewer pixels than expected",
+            ));
+        }
     }
 
     Ok(())