suppress "creating a shared reference to mutable static is discouraged" warnings

[Dicklessgreat]

The following warning messages have been observed when I build this project:

warning: creating a shared reference to mutable static is discouraged
  --> src/audio.rs:89:17
   |
89 |                 TX_BUFFER.initialize_all_copied(0);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ shared reference to mutable static
   |
   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
   = note: shared references to mutable statics are dangerous; it's undefined behavior if the static is mutated or if a mutable reference is created for it while the shared reference lives
   = note: `#[warn(static_mut_refs)]` on by default

warning: creating a shared reference to mutable static is discouraged
  --> src/audio.rs:90:34
   |
90 |                 let (ptr, len) = TX_BUFFER.get_ptr_len();
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^ shared reference to mutable static
   |
   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
   = note: shared references to mutable statics are dangerous; it's undefined behavior if the static is mutated or if a mutable reference is created for it while the shared reference lives

from discord discussion:
Corvus Prudens says:
This will probably take a little time to be resolved in the general ecosystem
really what we need as a direct replacement is SyncUnsafeCell, but that's currently unstable
(of course, for full safety, we have many options that introduce a bit of runtime checking like embedded mutexes)