feat(sdk): refuse npm runtime dependencies at build time

Plugins run in bare V8 - no fs, no net, no process, no Buffer - so an npm
package touching a Node API used to build green and die on a live CS2
server, far from its cause. assertNoNpmRuntimeDeps moves that failure to
build time, exempting @s2script/* builtins and workspace-linked code
(file:/workspace: ranges, or a symlink an npm workspaces install leaves
in node_modules).