libnpmexec: Programmatic npm exec API

libnpmexec provides a programmatic interface to the core functionality of `npm exec` (and by extension, `npx`). It enables developers to execute packages and binaries found in the local `node_modules/.bin` directory, npm cache, or fetched from the npm registry, without directly invoking the `npm` CLI. The package is currently at version 10.2.5 and is actively maintained as part of the broader npm CLI monorepo, with a healthy release cadence. Its key differentiator is offering a low-level, configurable API to manage the lifecycle of package execution, including argument parsing, cache management, and user prompts, making it suitable for tooling and automation that requires direct control over script execution. It forms the underlying mechanism for the `npx` command line utility, handling package resolution and environment setup.