Discover workspaces without using them in resolution (#3585)

Add minimal support for workspace discovery, only used for determining
paths in the bluejay commands.

We can now discover the workspace structure, namely that the
`pyproject.toml` of a package belongs to a workspace `pyproject.toml`
with members and exclusion. The globbing logic is inspired by cargo. We
don't resolve `workspace = true` metadata declarations yet.

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

@@ -0,0 +1,14 @@
+[project]
+name = "albatross"
+version = "0.1.0"
+dependencies = ["bird-feeder", "tqdm>=4,<5"]
+
+[tool.uv.sources]
+bird-feeder = { workspace = true }
+
+[tool.uv.workspace]
+members = ["packages/*"]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"