Bump workspace to edition 2024

- edition = "2024" in the workspace manifest and rsdosedit
- extern blocks must be unsafe: interrupts.rs ISR stubs -> unsafe extern "C"
- #[no_mangle] -> #[unsafe(no_mangle)] (efi_main, isr_dispatch)
- One missed static-mut read in free_list_insert wrapped in an explicit
  unsafe block (edition 2024 removed the implicit unsafe context inside
  unsafe fns)
- rustfmt reflows for 2024: nested if-lets become let-chains, imports
  re-sorted, rsdosedit help-screen box rows wrapped

No codegen-affecting changes. Validated: cargo check/clippy/fmt clean
(host + uefi target), make test-disk PASS, editor round-trip PASS.

1 files changed, 1 insertions, 1 deletions

diff --git a/rsnix/src/memory.rs b/rsnix/src/memory.rs
index 54ff7be..7c3eda0 100644
--- a/rsnix/src/memory.rs
+++ b/rsnix/src/memory.rs
@@ -89,7 +89,7 @@ fn align_up(x: usize, a: usize) -> usize {
 unsafe fn free_list_insert(block: *mut Header) {
     let addr = block as usize;
     let mut prev: *mut Header = ptr::null_mut();
-    let mut cur = FREE_LIST;
+    let mut cur = unsafe { FREE_LIST };
     while !cur.is_null() && (cur as usize) < addr {
         prev = cur;
         cur = unsafe { (*(*cur).links()).next };