fix: Clippy byte_char_slices lint failure on Rust 1.98

[rmems]

Problem

Scheduled CI has been failing since July 10, 2026. The failure is a new Clippy lint (byte_char_slices) introduced in Rust 1.97, now deny-by-default with -D warnings.

Error:

error: can be more succinctly written as a byte str
  --> src/gguf/cursor.rs:10:40
10 | pub(crate) const GGUF_MAGIC: [u8; 4] = [b'G', b'G', b'U', b'F'];
   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `*b"GGUF"`

Fix

In src/gguf/cursor.rs line 10, change:

pub(crate) const GGUF_MAGIC: [u8; 4] = [b'G', b'G', b'U', b'F'];

to:

pub(crate) const GGUF_MAGIC: [u8; 4] = *b"GGUF";

Context

• First failing run: 29066537784 (2026-07-10)
• Last passing run: 28990847741 (2026-07-09)
• Rust stable updated from 1.96 to 1.97 around that time
• Lint reference: https://rust-lang.github.io/rust-clippy/rust-1.97.0/index.html#byte_char_slices

[linear-code]

LIM-779

LIM-780