fix: remove node_shim exec dependency (#34739)
## Summary
- Removes the Unix-only `exec` crate from `node_shim` and uses the
standard library process exec support instead.
- Preserves the existing `argv[0]` behavior by passing the translated
shim name through `CommandExt::arg0` before replacing the process.
- Updates the lockfile so the removed dependency and its now-unused
transitive entries are no longer resolved for this crate.
## Validation
- `cargo check -p node_shim`
- `cargo test -p node_shim`
- `cargo build -p node_shim --target=x86_64-unknown-linux-gnu`
- `cargo tree -p node_shim --target=x86_64-unknown-linux-gnu -e normal
--prefix none | sort -u | wc -l`
- Smoke-tested the built shim through a `node` symlink with `-e
'console.log(process.argv0)'` to confirm it still reports `node`.
- Compared the debug `node_shim` binary size before and after the
dependency removal on the same Linux target.
Co-authored-by: Nathan Whitaker <nathan@deno.com>
