OpenVMM Rust 2024 Compatibility

[smalis-msft]

Tracking issue for known problems that will prevent OpenVMM from adopting the Rust 2024 edition once it is released. Ideally we will fully turn on the rust-2024-compatibility lint and remove all allows before making the switch.

• linkme::distributed_slice: unsafe-attr-outside-unsafe 2024 compat lint is unfixable dtolnay/linkme#101 (unsafe-attr-outside-unsafe)
• linkme v0.3.25 and up fire clippy::ref-option-ref when constructing a slice of Option<&'static Foo> dtolnay/linkme#103
• Calls to std::env::set_var and remove_var are becoming unsafe. They should either be removed or audited (deprecated-safe-2024)
  • Fix the one allow in mesh
• The changes to lifetime capture rules will need to be audited on each individual case (impl_trait_overcaptures)
• The changes to drop order need to be thought through (tail-expr-drop-order, if-let-rescope)
• The changes to macro parsing will need to be audited on each individual case (edition_2024_expr_fragment_specifier)
• Safety comments for unsafe attributes (Unsafe attributes support (undocumented_unsafe_blocks) rust-lang/rust-clippy#13316)
• Take the style edition formatting changes