Add URI-based programmatic launch for Protein Viewer from CLI/Python

[Copilot]

This change adds a programmatic way to open one or more local structure files in Protein Viewer without Explorer selection, enabling shell/Python-driven workflows. It introduces a stable VS Code deep-link entrypoint and aligns command handling for single- and multi-file invocation.

• Programmatic launch surface

  • Register onUri activation and a URI handler in the extension.
  • Support deep links of the form:
    • vscode://ArianJamasb.protein-viewer/open?file=<path-or-uri>&file=<path-or-uri>
  • Parse repeated file query parameters and open them in a new Protein Viewer tab.

• Command path hardening

  • Update protein-viewer.activateFromFiles to handle both:
    • Explorer multi-select (selectedFiles)
    • Single-file invocation (file_uri fallback)

• Documentation updates

  • Add concise CLI/Python usage examples in README for constructing and opening deep links with multiple files.

• Focused parsing coverage

  • Add targeted tests for URI parsing behavior (/open path handling and repeated file params).

import urllib.parse, webbrowser

files = ["/abs/a.pdb", "/abs/b.cif"]
query = "&".join(f"file={urllib.parse.quote(f)}" for f in files)
webbrowser.open(f"vscode://ArianJamasb.protein-viewer/open?{query}")