Simplify CLI integration by using the new spawn function instead of manually managing CLI paths and spawning processes.

[Karan-Palan]

fixes #130

[augmentcode]

🤖 Augment PR Summary

Summary: Refactors the VS Code extension’s CLI integration to use the new @sourcemeta/jsonschema spawn() helper instead of manually resolving the CLI script path and spawning Node.

Changes:

• Simplified CommandExecutor to call spawn(args) and map its stdout/stderr + exit code into CommandResult.
• Updated extension activation to construct CommandExecutor without extensionPath.
• Adjusted the VS Code extension test to assert only on error-severity diagnostics for HTTP $ref cases.
• Updated VS Code build/deps: externalized @sourcemeta/jsonschema in esbuild and bumped the dependency to ^13.3.0.

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[augmentcode]

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[jviotti]

Are you sure we need this? I think the package step will do this already

[Karan-Palan]

The CI fails without it. The extension runs from build/vscode/extension.js which requires @sourcemeta/jsonschema from node_modules. We marked it as external in esbuild (as it is 28mb), so build/vscode/node_modules must exist before tests run.

[jviotti]

OK, I guess that's fine. Maybe someday we revamp this with CMake 😅