This change updates the Embedonomicon to the new Rust edition 2024.
Up until now, most of the book targeted the Rust edition 2018.

Edition 2024 brings a set of new features that remove the need for
nightly toolchains. Another advantage is that it introduces the
readers to the current language changes, like the unsafe `no_mangle`
and `export_name` attributes.

This commit bundles the following changes:
- Update the CI workflow to work with Rust edition 2024 and remove the
  need for the nightly toolchain.
- Adapt all `Cargo.toml` manifests to use edition 2024.
- Update all disassemblies and vector table dumps after compiling with
  the 1.89 toolchain and edition 2024. This also adds instruction
  addresses to some of the disassemblies, since the text referred to
  them but they were not present (see the exceptions chapter and the asm
  chapter).
- Add `unsafe` to the `no_mangle`, `export_name` and `link_section`
  attributes.
- Add `unsafe` to `extern` blocks, marking pure Rust functions as `safe`.
- Remove use of `core::intrinsics` and use a single `asm!` instruction
  to trigger UDF. The reasoning behind this is that `core::intrinsics`
  requires nightly and is only meant to be used by the compiler. The
  assembly line achieves the same effect.
- Make sure all tests are executed (including the exception tests, which
  were disabled in the past).
- Update the singleton example and tests to use `cortex_m::interrupt::mutex`
  as suggested by an existing TODO. This removes the need for some
  unsafe. Also use more recent versions of the `cortex-m` and
  `cortex-m-semihosting` crates.
- `rust_begin_unwind` is in the `__rustc` module now.
- Update text in most chapters to describe the new changes in edition
  2024.

A follow up change will be created to move away from `.data` and `.bss`
section initialization using Rust code. Most runtime crates have moved
away from this due to certain soundness challenges, so the Embedonomicon
should also inform about them.