Add npm run ava command, update instructions, and exclude files from VSCode search

[mbg]

A few minor bits bundled up:

• Adds a npm run ava command; which can be used to run tests based on a custom path.
• Updates npm run test to use that, with the existing src/ path.
• Updates CONTRIBUTING.md to highlight npm run ava
• Updates the justfile to use npm run ava
• Filters transpiled files and node_modules from search results in VSCode

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull Request Overview

This PR adds development tooling improvements to streamline test execution and improve the development experience. It introduces a flexible npm run ava command for running tests on custom paths, while maintaining backward compatibility with the existing test workflow.

• Adds a new npm run ava script to enable flexible test path specification
• Updates existing npm run test to use the new script with default src/ path
• Updates documentation and justfile to reference the new command
• Excludes transpiled files from VSCode search results

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
package.json	Adds ava script and updates test script to use it with default path
lib/*.js	Auto-generated JavaScript files reflecting package.json changes
justfile	Updates test_file recipe to use new npm script
CONTRIBUTING.md	Documents the new testing command for specific paths
.vscode/settings.json	Excludes build artifacts from search results