Replace std::time::Instant with web_time::Instant (#14668)

# Description
The `std::time::Instant` type panics in the WASM context. To prevent
this, I replaced all uses of `std::time::Instant` in WASM-relevant
crates with `web_time::Instant`. This ensures commands using `Instant`
work in WASM without issues. For non-WASM targets, `web-time` simply
reexports `std::time`, so this change doesn’t affect regular builds
([docs](https://docs.rs/web-time/latest/web_time/)).

To ensure future code doesn't reintroduce `std::time::Instant` in WASM
contexts, I added a `clippy wasm` command to the toolkit. This runs
`cargo clippy` with a `clippy.toml` configured to disallow
`std::time::Instant`. Since `web-time` aliases `std::time` by default,
the `clippy.toml` is stored in `clippy/wasm` and is only loaded when
targeting WASM. I also added a new CI job that tests this too.

# User-Facing Changes

None.

crates/nu-command/Cargo.toml

@@ -106,6 +106,7 @@ wax = { workspace = true }
 which = { workspace = true, optional = true }
 unicode-width = { workspace = true }
 data-encoding = { version = "2.6.0", features = ["alloc"] }
+web-time = { workspace = true }
 
 [target.'cfg(windows)'.dependencies]
 winreg = { workspace = true }

crates/nu-command/src/debug/timeit.rs

@@ -1,6 +1,6 @@
 use nu_engine::{command_prelude::*, ClosureEvalOnce};
 use nu_protocol::engine::Closure;
-use std::time::Instant;
+use web_time::Instant;
 
 #[derive(Clone)]
 pub struct TimeIt;

crates/nu-command/src/viewers/table.rs

@@ -20,9 +20,9 @@ use std::{
     io::{IsTerminal, Read},
     path::PathBuf,
     str::FromStr,
-    time::Instant,
 };
 use url::Url;
+use web_time::Instant;
 
 const STREAM_PAGE_SIZE: usize = 1000;