fix #51: support Dart workspaces with multiple pubspec files

[BIOMAS-Devel]

Summary

This fixes support for Dart/Flutter workspaces where multiple pubspec.yaml files may exist above a file.

Problem

The extension currently expects to find exactly one pubspec.yaml above a Dart file.
In Dart workspaces / monorepos, this is not always valid because both the workspace root and the package root may contain a pubspec.yaml.

This causes errors such as:

Expected to find a single pubspec.yaml file above ..., 2 found.

Fix

Instead of throwing when multiple pubspec.yaml files are found, the extension now selects the nearest matching pubspec.yaml for the file when 1 or 2 files are found (3 or more is still considered an error).

This preserves the expected behavior for single-package projects and allows the extension to work correctly in monorepos/workspaces.

Notes

I was able to verify the fix locally against the workspace scenario that triggered the bug.

I also hit some unrelated test/repo setup issues while trying to run the full test flow, so I’m documenting that here in case it helps review:

• comments in tsconfig.json where not parsed correctly
• had to "npm uninstall tsc" and then "npm install" to be able to run "npm run package" and generate the vsix

Should close #51.