Fix: uv tool install installs workspace members non‑editable by default; --editable to opt‑in

[krishmas]

Summary

Resolves #16306

• Default non‑editable for workspace deps in tool installs
  • Tools no longer get editable .pth links to workspace members; installs are self‑contained.
  • Passing --editable makes both the target package and workspace members editable.
• Share editable conversion across commands
  • Move editable conversion into apply_editable_mode and reuse from both sync and tool install

Test Plan

• Tool install integration tests
  • Default non‑editable workspace member (tool_install::tool_install_no_editable_workspace_member):
  • Explicit --editable (tool_install::tool_install_workspace_editable):
• Locally used built uv with the Python project mentioned in #16306 and observed that changes to workspace dependency source code no longer changed tool behavior unless --editable was used