fix: honour editable = true in transitive [tool.uv.sources] at install time

[earlybard]

What

editable = true on a path dependency's [tool.uv.sources] entry is now honoured when pixi installs the environment.

This is a follow-up to #6121: that fix resolves path dependencies with editable: None so a manifest declaration and a transitive [tool.uv.sources] entry can't conflict during the uv solve, and the lock file doesn't record editability at all. The side effect was that a transitive editable = true was silently dropped — uv honoured it while resolving, but the installed package was always non-editable unless the workspace manifest itself declared it editable.

How

Editability stays an install-time property, derived from what's declared on disk at that moment:

1. The workspace manifest wins for packages it declares as path dependencies. A path spec without an editable key counts as non-editable, matching uv.
2. For packages the manifest doesn't declare, pixi reads the locked path packages' own pyproject.tomls and applies their [tool.uv.sources] editable = true declarations.

The lookup is best-effort: installing from a lock skips resolution, so a pyproject.toml that is missing, has drifted since the solve, or uses a [tool.uv] schema this version of uv doesn't know is skipped, and the package installs non-editable exactly as it did before.

AI Disclosure

Written with Claude Opus + Fable, reviewed and edited by me.