Summary

• extend the interpreter environment query to scan .dist-info/direct_url.json metadata for PEP 610 editable installs
• append editable file:// source roots, plus a conventional src/ child when present, to interpreter-derived import paths
• keep the scan bounded and tolerant of missing, invalid, non-editable, or non-file direct_url metadata
• add a Windows-runnable regression test that executes the same interpreter query script with a synthetic editable install

Closes #1843.

Test plan

• cargo +stable-x86_64-pc-windows-gnu fmt --all --check
• cargo +stable-x86_64-pc-windows-gnu test -p pyrefly_config environment::environment -- --nocapture
• cargo +stable-x86_64-pc-windows-gnu test -p pyrefly_config
• cargo +stable-x86_64-pc-windows-gnu check -p pyrefly
• cargo +stable-x86_64-pc-windows-gnu test -p pyrefly --test pyrefly_lsp_interaction_tests configuration -- --nocapture
• CLI smoke: flat-layout editable package with only direct_url.json metadata now checks with 0 errors
• CLI smoke: src/ layout editable package with only direct_url.json metadata now checks with 0 errors