Build backend: Revamp include/exclude (#9525)

When building the source distribution, we always need to include
`pyproject.toml` and the module, when building the wheel, we always
include the module but nothing else at top level. Since we only allow a
single module per wheel, that means that there are no specific wheel
includes. This means we have source includes, source excludes, wheel
excludes, but no wheel includes: This is defined by the module root,
plus the metadata files and data directories separately.

Extra source dist includes are currently unused (they can't end up in
the wheel currently), but it makes sense to model them here, they will
be needed for any sort of procedural build step.

This results in the following fields being relevant for inclusions and
exclusion:

* `pyproject.toml` (always included in the source dist)
* project.readme: PEP 621
* project.license-files: PEP 639
* module_root: `Path`
* source_include: `Vec<Glob>`
* source_exclude: `Vec<Glob>`
* wheel_exclude: `Vec<Glob>`
* data: `Map<KnownDataName, Path>`

An opinionated choice is that that wheel excludes always contain the
source excludes: Otherwise you could have a path A in the source tree
that gets included when building the wheel directly from the source
tree, but not when going through the source dist as intermediary,
because A is in source excludes, but not in the wheel excludes. This has
been a source of errors previously.

In the process, I fixed a bug where we would skip directories and only
include the files and were missing license due to absolute globs.

scripts/packages/built-by-uv/data-dir/build-script.py

@@ -0,0 +1 @@
+print("Build script (currently unused)")

scripts/packages/built-by-uv/pyproject.toml

@@ -7,7 +7,15 @@ requires-python = ">=3.12"
 dependencies = ["anyio>=4,<5"]
 license-files = ["LICENSE*", "third-party-licenses/*"]
 
-[tool.uv.wheel.data]
+[tool.uv.build-backend]
+# A file we need for the source dist -> wheel step, but not in the wheel itself (currently unused)
+source-include = ["data/build-script.py"]
+# A temporary or generated file we want to ignore
+source-exclude = ["/src/built_by_uv/not-packaged.txt", "__pycache__", "*.pyc", "*.pyo"]
+# Headers are build-only
+wheel-exclude = ["build-*.h"]
+
+[tool.uv.build-backend.data]
 scripts = "scripts"
 data = "assets"
 headers = "header"

scripts/packages/built-by-uv/src/built_by_uv/build-only.h

@@ -0,0 +1,4 @@
+// There is no build step yet, but we're already modelling the basis for it by allowing files only in the source dist,
+// but not in the wheel.
+
+#include <pybind11/pybind11.h>

scripts/packages/built-by-uv/src/built_by_uv/not-packaged.txt

@@ -0,0 +1 @@
+This file should only exist locally.