Refactor the imp/gui bondary to use real traits (#18)

# Summary

Introduces a trait-based platform abstraction layer that makes the boundary
between platform-specific and shared code explicit and compile-time verified.

The TLDR version of this new trait stuff works:

1. Define a `PlatformInterface` trait.
2. Each platform defines a zero-sized struct implementing the trait (ex `WebPlatform`).
3. Create an ifdef'd type alias on those structs:

```rust
#[cfg(feature = "web")]
pub type Platform = web::WebPlatform;

#[cfg(all(feature = "desktop"))]
pub type Platform = desktop::DesktopPlatform;

#[cfg(all(feature = "mobile", not(feature = "web")))]
pub type Platform = mobile::MobilePlatform;
```

5. Add a compile time assertion that `Platform` implements `PlatformInterface`.

#  Motivation

Previously, platform code used a mix of pub use re-exports and #[cfg] blocks
that made it difficult to understand what each platform must implement. The
new trait-based approach provides:

- Clear documentation of the platform contract
- Compile-time verification that all platforms implement required
  functionality
- Ability to cargo check without feature flags (via stub platform)

# Changes

New traits in imp/mod.rs:
  - PlatformInterface - logging, permissions, network, config, storage. Overall this the trait that platforms must satify to compile.
  - AudioSystemInterface - audio system initialization and recording
  - AudioPlayerInterface - opus audio playback

 Type aliases:
  - Platform, AudioSystem, AudioPlayer resolve to the correct types based on
  feature flags

Call site updates:
  - Changed from imp::function() to Platform::function() syntax
  - Removed ImpRead/ImpWrite helper traits in favor of direct bounds

# Testing

Manual testing reveals that Web and Desktop still work, I (Liam) have not tested the mobile version beyond compilation.

Co-authored-by: Liam Warfield <liam.warfield@gmail.com>
Reviewed-on: #18
Co-authored-by: Sam Sartor <me@samsartor.com>
Co-committed-by: Sam Sartor <me@samsartor.com>

gui/src/lib.rs

@@ -7,11 +7,12 @@ use asynchronous_codec::FramedWrite;
 use color_eyre::eyre::{bail, Error};
 use dioxus::prelude::*;
 use futures::select;
+use futures::AsyncRead;
+use futures::AsyncWrite;
 use futures::FutureExt as _;
 use futures::SinkExt as _;
 use futures::StreamExt as _;
 use futures_channel::mpsc::UnboundedSender;
-pub use imp::spawn;
 use msghtml::process_message_html;
 use mumble_protocol::control::msgs;
 use mumble_protocol::control::ControlCodec;
@@ -27,7 +28,10 @@ use tracing::error;
 use tracing::info;
 
 use crate::effects::AudioProcessor;
-use crate::imp::AudioSystem;
+use crate::imp::{
+    AudioPlayer, AudioPlayerInterface as _, AudioSystem, AudioSystemInterface as _, Platform,
+    PlatformInterface as _,
+};
 
 pub mod app;
 mod effects;
@@ -47,7 +51,9 @@ pub async fn network_entrypoint(mut event_rx: UnboundedReceiver<Command>) {
 
         *STATE.server.write() = Default::default();
         *STATE.status.write() = ConnectionState::Connecting;
-        if let Err(error) = imp::network_connect(address, username, &mut event_rx, &config).await {
+        if let Err(error) =
+            Platform::network_connect(address, username, &mut event_rx, &config).await
+        {
             error!("could not connect {:?}", error);
             *STATE.status.write() = ConnectionState::Failed(error.to_string());
         } else {
@@ -56,7 +62,7 @@ pub async fn network_entrypoint(mut event_rx: UnboundedReceiver<Command>) {
     }
 }
 
-pub async fn network_loop<R: imp::ImpRead, W: imp::ImpWrite>(
+pub async fn network_loop<R: AsyncRead + Unpin + 'static, W: AsyncWrite + Unpin + 'static>(
     username: String,
     event_rx: &mut UnboundedReceiver<Command>,
     mut reader: FramedRead<R, ControlCodec<Serverbound, Clientbound>>,
@@ -105,12 +111,12 @@ pub async fn network_loop<R: imp::ImpRead, W: imp::ImpWrite>(
                     break;
                 }
 
-                imp::sleep(Duration::from_millis(3000)).await;
+                Platform::sleep(Duration::from_millis(3000)).await;
             }
         });
     }
 
-    let mut audio = imp::AudioSystem::new().await?;
+    let mut audio = AudioSystem::new().await?;
     {
         let send_chan = send_chan.clone();
         let mut sequence_num = 0;
@@ -296,8 +302,8 @@ fn accept_command(
 
 fn accept_packet(
     msg: ControlPacket<mumble_protocol::Clientbound>,
-    audio_context: &mut imp::AudioSystem,
-    player_map: &mut HashMap<u32, imp::AudioPlayer>,
+    audio_context: &mut AudioSystem,
+    player_map: &mut HashMap<u32, AudioPlayer>,
 ) -> Result<(), Error> {
     match msg {
         ControlPacket::UDPTunnel(u) => {