linera-base: expunge wasmtimer in favour of kywasmtime (#4561)

## Motivation

We ran into a variant of
whizsid/wasmtimer-rs#22, which was drastically
slowing down the operation of `@linera/client` (see #4444 for details).
Additionally, `wasmtimer` doesn't look thread-safe: it uses
[`parking_lot`](https://crates.io/crates/parking_lot), which will panic
on Wasm if the lock ever tries to park.

## Proposal

Replace our dependency on `wasmtimer` with a [Linera
fork](https://github.com/linera-io/kywasmtime/) of
[`kywasmtime`](https://github.com/rom1v/kywasmtime), a package that
exposes the same API but using the browser `clearTimeout` APIs instead
of implementing its own priority queue.

I made a couple of patches to be more helpful for our usage, which are
PR'd upstream as rom1v/kywasmtime#3 and
rom1v/kywasmtime#4.

Since `kywasmtime` isn't published to crates.io, we use it as a git
dependency. This is okay, since `linera-web` is also never published to
crates.io (only to npm), and the SDK crates that we do publish don't
rely on it.

## Test Plan

Manually tested.

## Release Plan

- These changes should be backported to the latest `testnet` branch,
then
    - be released in a new SDK.

## Links

- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)
- Fixes #4444.

Author: Twey

Cargo.lock

@@ -271,7 +271,6 @@ wasmtime = { version = "25.0.0", default-features = false, features = [
     "runtime",
     "std",
 ] }
-wasmtimer = "0.2.0"
 web-sys = "0.3.69"
 web-time = "1.1.0"
 wit-bindgen = "0.24.0"
@@ -328,6 +327,10 @@ default-features = false
 features = ["rt-tokio", "rustls"]
 version = "1.76.0"
 
+[workspace.dependencies.kywasmtime]
+git = "https://github.com/linera-io/kywasmtime"
+rev = "480df00badbe80520d5b990855138d3638c56159"
+
 [profile.release]
 lto = "thin"
 debug = true

Cargo.toml

@@ -21,16 +21,16 @@ revm = []
 test = ["test-strategy", "proptest"]
 web = [
     "getrandom/js",
+    "kywasmtime",
     "rand/getrandom",
     "rand/std",
     "rand/std_rng",
     "tracing-web",
-    "wasmtimer",
     "wasm-bindgen",
     "wasm-bindgen-futures",
     "wasm_thread",
-    "web-time",
     "web-sys",
+    "web-time",
 ]
 
 [dependencies]
@@ -50,6 +50,7 @@ getrandom = { workspace = true, optional = true }
 hex.workspace = true
 is-terminal.workspace = true
 k256.workspace = true
+kywasmtime = { workspace = true, optional = true }
 linera-witty = { workspace = true, features = ["macros"] }
 prometheus = { workspace = true, optional = true }
 proptest = { workspace = true, optional = true, features = ["alloc"] }
@@ -70,7 +71,6 @@ trait-variant.workspace = true
 wasm-bindgen = { workspace = true, optional = true }
 wasm-bindgen-futures = { workspace = true, optional = true }
 wasm_thread = { workspace = true, optional = true }
-wasmtimer = { workspace = true, optional = true }
 web-sys = { workspace = true, optional = true }
 web-time = { workspace = true, optional = true }
 

linera-base/Cargo.toml

@@ -7,8 +7,10 @@ Abstractions over time that can be used natively or on the Web.
 
 cfg_if::cfg_if! {
     if #[cfg(web)] {
+        // This must remain conditional as otherwise it pulls in JavaScript symbols
+        // on-chain (on any Wasm target).
         pub use web_time::*;
-        pub use wasmtimer::tokio as timer;
+        pub use kywasmtime as timer;
     } else {
         pub use std::time::*;
         pub use tokio::time as timer;