Initial workspace support (#3705)

Add workspace support when using `-r <path>/pyproject.toml` or `-e
<path>` in the pip interface. It is limited to all-editable
static-metadata workspaces, and tests only include a single main
workspace, ignoring path dependencies in another workspace. This can be
considered the MVP for workspace support: You can create a workspace,
you can install from it, but some options and conveniences are still
missing. I'll file follow-up tickets (support in lockfiles, support path
deps in other workspace, #3625)

There is also support in `uv run`, but we need
https://github.com/astral-sh/uv/issues/3700 first to properly support
using different current projects in the bluejay interface, currently the
resolution and therefore the lockfile depends on the current project.
I'd do this change first (it's big enough already), then #3700, and then
add workspace support properly to bluejay.

Fixes #3404

scripts/workspaces/albatross-root-workspace/packages/seeds/pyproject.toml

@@ -1,7 +1,7 @@
 [project]
 name = "seeds"
 version = "1.0.0"
-dependencies = ["boltons==24.0.0"]
+dependencies = ["idna==3.6"]
 
 [build-system]
 requires = ["hatchling"]

scripts/workspaces/albatross-root-workspace/packages/seeds/src/seeds/__init__.py

@@ -1,4 +1,4 @@
-import boltons
+import idna
 
 
 def seeds():

scripts/workspaces/albatross-virtual-workspace/packages/seeds/pyproject.toml

@@ -1,7 +1,7 @@
 [project]
 name = "seeds"
 version = "1.0.0"
-dependencies = ["boltons==24.0.0"]
+dependencies = ["idna==3.6"]
 
 [build-system]
 requires = ["hatchling"]

scripts/workspaces/albatross-virtual-workspace/packages/seeds/src/seeds/__init__.py

@@ -1,4 +1,4 @@
-import boltons
+import idna
 
 
 def seeds():