Declare the AVAudioSession dependencies on visionOS

[SkeletonGamer]

The CoreAudio backend gates its AVAudioSession code path on every non-macOS Apple platform:

#[cfg(all(target_vendor = "apple", not(target_os = "macos")))]

but block2, objc2-foundation and objc2-avf-audio are declared only for ios and tvos.
On visionOS the code is compiled while the crates are absent, so the build stops at:

error[E0432]: unresolved import `objc2_avf_audio`
error[E0432]: unresolved import `block2`
error[E0432]: unresolved imports `objc2_foundation::NSNotification`, `objc2_foundation::NSNotificationCenter`

This looks like an oversight in #1155, which added tvos to that list. Everything below is already
in place: coreaudio-rs gained visionOS support in RustAudio/coreaudio-rs#148, and mach2 0.6, the
version cpal requires, builds for every Apple vendor.

Builds, on master with rustc 1.97 and Xcode 26.6:

target	before	after
aarch64-apple-darwin	ok	ok
aarch64-apple-ios	ok	ok
aarch64-apple-tvos	ok	ok
aarch64-apple-visionos	fails to build	ok

Runtime, on the visionOS 26.2 simulator (xcrun simctl spawn), built for
aarch64-apple-visionos-sim:

• examples/enumerate reports the CoreAudio host and the default device, 48 kHz, F32, 2 channels out.
• examples/beep opens an output stream and the sine is audible.
• rodio at master, which already requires cpal 0.18, plays a SineWave through
  DeviceSinkBuilder::open_default_sink and exits cleanly.

I have not run this on Vision Pro hardware, only on the simulator.

I did not widen the cfg to all(target_vendor = "apple", not(target_os = "macos")), which is what
the code gate says. watchOS still fails further down inside coreaudio-rs
(cannot find value buffer_frame_size), so claiming it in the manifest would only move the error.
Adding visionos alone keeps the manifest honest about what builds today.

[SkeletonGamer]

The failing clippy-Linux and clippy-Windows checks are unrelated to this PR, which only touches
Cargo.toml and CHANGELOG.md. clippy::question_mark now fires on src/host/alsa/mod.rs:610 and
src/host/asio/device.rs:183 with Rust 1.97, released yesterday, and CI runs with -D warnings.
#1261 hits the same failure, and the runs that predate 1.97 are green.

#1263 fixes both.

[roderickvd]

Thanks! Made some minor edits to the changelog and readme. Merging now.