`oxlint::lint` is exposed via napi and can therefore be invoked more
than once in the same Node process (e.g. from a long-lived linter
daemon, a build-tool worker, or an LSP host). Today the second call
panics in one of three places:

1. `init_tracing` calls `.init()` on a `tracing_subscriber::registry()`,
   which internally `set_global_default(...).unwrap()`s. The second
   call returns `Err(SetGlobalDefaultError("a global default trace
   dispatcher has already been set"))` and panics.
2. `init_miette` calls `miette::set_hook(...).unwrap()`. `set_hook`
   returns `Err` if a hook is already installed, so it panics on the
   second call.
3. `LintCommand::init_rayon_thread_pool` calls
   `rayon::ThreadPoolBuilder::new()...build_global().unwrap()`. The
   second call returns
   `Err(ThreadPoolBuildError { kind: GlobalPoolAlreadyInitialized })`
   and panics.

All three are one-shot global inits that should silently no-op on
repeat invocation. Wrap the first two in a `OnceLock` and discard the
result; replace the `.unwrap()` on `build_global` with `let _ = ...`.

`oxfmt` already uses the same `OnceLock` + `try_init` pattern at
`apps/oxfmt/src/core/utils.rs`, so this brings oxlint in line.

Caveat for users: rayon's global pool keeps the thread count from the
first call. Subsequent calls with a different `--threads` value are
silently ignored. That matches rayon's documented semantics and is the
only sensible behaviour without tearing down and recreating the pool.

This change unblocks the daemon-style worker pattern at
https://github.com/MatissJanis/oxlint-lage-repro, which on the Datadog
web-ui codebase (~7,500 packages) cuts cold-cache lint runtime from
~20 minutes to ~10 minutes by amortising oxlint's ~1.6s startup across
many packages handled by the same lage worker thread.

Address review feedback on oxc-project#21899. Now that the panic-prone init
calls live inside `OnceLock::get_or_init`, the closure runs at most
once per process, so the inner result is safe to `.unwrap()` instead
of swallowing with `let _ = ...`. Also wrap the rayon `build_global`
call in its own `OnceLock` so it follows the same pattern.

…entrant-lint

# Conflicts:
#	apps/oxlint/src/command/lint.rs