feat(iroh): Make iroh compile to wasm32-unknown-unknown (#3189)

## Description

(This PR is a rebase & some changes from the #3145 PR, so we don't
disturb users who are trying out the iroh browser alpha.)

- Adds a bunch of `#[cfg(not(wasm_browser))]` to anything related to
socket networking (UDP sockets, DNS, etc.)
- Implements a `WebRuntime` for quinn to use instead of `TokioRuntime`
in browsers
- Implements sleeping & timing utilities for `backoff` that work in
browsers
- Moves `node_info` out of the `dns` module, so we can disable `dns` as
a whole, but keep `node_info` for discovery
- Disables `MappedAddr::Ip` in browsers
- Adjusts dependencies so we don't depend on unused/unsupported things
in browsers

## Breaking Changes

- `iroh-relay`: The `iroh_relay::dns::node_info` module was moved to
`iroh_relay::node_info`

## Notes & open questions

I'm holding off on refactoring bigger parts for now. I have two main
ideas:
- Group a bunch of structs in `magicsock.rs`, i.e. everything that
depends on sockets.
However, to do this, I want to refactor the way we *sometimes* use
`Arc<netwatch::UdpSocket>` and *sometimes* use `UdpConn`, which is just
a newtype over said type.
Ideally we store `Arc<netwatch::UdpSocket>` everywhere, since it's more
commonly used in APIs, e.g. in iroh-net-report, and only use `UdpConn`,
when we need the udp sockets to implement `AsyncUdpSocket` from quinn.
- Refactor the `node_info` module so there's fewer places that depend on
`DnsResolver` in it.
There's a bunch of things in that module that IMO are needless
indirections (we go from `hickory::TxtLookup` ->
`node_info::TxtAttrs<IrohAttr>` -> `(NodeId, NodeData)` -> `NodeInfo`.
And even then, `NodeInfo` is mostly isomorphic to `NodeAttr`).

I think both these refactors are helpful, but don't necessarily make the
diff easier to read? Not sure. I'd like to merge this & then work on
these refactors next week.

## Change checklist

- [x] Self-review.
- [x] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [x] Tests if relevant.
- [x] All breaking changes documented.

Author: matheus23

.cargo/config.toml

@@ -0,0 +1,2 @@
+[target.wasm32-unknown-unknown]
+runner = "wasm-bindgen-test-runner"

.github/workflows/ci.yml

@@ -147,19 +147,30 @@ jobs:
         env:
           RUST_LOG: ${{ runner.debug && 'TRACE' || 'DEBUG' }}
 
-  wasm_build:
-    name: Build wasm32
+  wasm_test:
+    name: Build & test wasm32 for browsers
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
         uses: actions/checkout@v4
 
+      - name: Setup node.js version 22.5 # needed for browser-like websocket API support in node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22.5
+
       - name: Install stable toolchain
         uses: dtolnay/rust-toolchain@stable
 
       - name: Add wasm target
         run: rustup target add wasm32-unknown-unknown
 
+      - name: Install cargo-binstall
+        uses: cargo-bins/cargo-binstall@main
+      
+      - name: Install wasm-bindgen-test-runner
+        run: cargo binstall wasm-bindgen-cli --locked --no-confirm
+
       - name: Install wasm-tools
         uses: bytecodealliance/actions/wasm-tools/setup@v1
 
@@ -172,18 +183,25 @@ jobs:
       - name: wasm32 build (iroh-net-report)
         run: cargo build --target wasm32-unknown-unknown -p iroh-net-report --no-default-features
 
+      - name: wasm32 build (iroh)
+        run: cargo build --target wasm32-unknown-unknown -p iroh --no-default-features
+
       # If the Wasm file contains any 'import "env"' declarations, then
       # some non-Wasm-compatible code made it into the final code.
       - name: Ensure no 'import "env"' in iroh-relay Wasm
         run: |
           ! wasm-tools print --skeleton target/wasm32-unknown-unknown/debug/iroh_relay.wasm | grep 'import "env"'
 
-      # If the Wasm file contains any 'import "env"' declarations, then
-      # some non-Wasm-compatible code made it into the final code.
       - name: Ensure no 'import "env"' in iroh-net-report Wasm
         run: |
           ! wasm-tools print --skeleton target/wasm32-unknown-unknown/debug/iroh_net_report.wasm | grep 'import "env"'
-      
+
+      - name: Ensure no 'import "env"' in iroh Wasm
+        run: |
+          ! wasm-tools print --skeleton target/wasm32-unknown-unknown/debug/iroh.wasm | grep 'import "env"'
+
+      - name: Run integration test in wasm
+        run: cargo test -p iroh --test integration --target=wasm32-unknown-unknown --no-default-features
 
   check_semver:
     runs-on: ubuntu-latest