Enable auto-rebuild in scikit-build-core at import time (#27)

Closes MET-41

## Summary of Changes

`scikit-build-core` has an `editable.rebuild` option, which can
automatically invoke CMake under the hood when we import from
`genmetaballs` to rebuild the C++ extension if needed. To use this
option, we need to turn off build isolation for our package so that
scikit build can use the right set of tools (see
scikit-build/scikit-build-core#1112 (comment)).
On the other hand, this also makes rebuilding a lot faster because Pixi
doesn't have to re-create a new isolated environment and build from
scratch.

See [`scikit-build-core`'s official doc on editable install for more
details](https://scikit-build-core.readthedocs.io/en/latest/configuration/index.html#editable-installs).

With this change, we shouldn't need to manually run `pixi reinstall
genmetaballs` anymore. Hopefully this will make our development
experience a bit smoother :).

## Test Plan

After enabling this option & run `pixi reinstall genmetaballs` one last
time just to make sure that the config is active. Then, I tried
modifying a couple of the C++ files, then run `pixi run test`
immediately after (without running `reinstall` manually), and the
changes are correctly reflected on the Python test results.

Author: horizon-blue

.pre-commit-config.yaml

@@ -27,7 +27,7 @@ repos:
       - id: test
         name: Run all tests
         # reinstall genmetaballs to rebuild C++/CUDA code, then run tests
-        entry: bash -c "pixi reinstall genmetaballs && pixi run test"
+        entry: pixi run test
         language: system
         pass_filenames: false
         always_run: true

pixi.lock

@@ -39,18 +39,23 @@ ninja = "*"
 scikit-build-core = "*"
 nanobind = "*"
 gtest = ">=1.17.0,<2"
-clang-tools = ">=18,<20"  # Includes clang-format and clang-tidy
+clang-tools = ">=18,<20" # Includes clang-format and clang-tidy
 mesalib = ">=25.0.5,<26"
 
 [tool.pixi.pypi-dependencies]
 genmetaballs = { path = ".", editable = true }
 ruff = ">=0.8.0"
 pre-commit = ">=3.0.0"
 
+[tool.pixi.pypi-options]
+# Disable build isolation for genmetaballs to allow scikit-build to find cmake and other build tools
+# See https://github.com/scikit-build/scikit-build-core/issues/1112#issuecomment-3025463521
+no-build-isolation = ["genmetaballs"]
+
 [tool.pixi.tasks]
 ctest = "ctest --test-dir build"
 pytest = "pytest"
-test = { depends-on = ["ctest", "pytest"] }
+test = { depends-on = ["pytest", "ctest"] }
 # Simple lint/format/fix commands (C++/CUDA + Python)
 format = { cmd = "scripts/format.sh" }
 lint = { cmd = "scripts/lint.sh" }
@@ -66,6 +71,7 @@ wheel.py-api = "cp313"                             # Or your Python version
 wheel.packages = ["genmetaballs/src/genmetaballs"]
 # use a persistent build directory to speed up rebuild & testing
 build-dir = "build"
+editable.rebuild = true
 
 [dependency-groups]
 dev = ["pytest"]
@@ -86,20 +92,20 @@ line-ending = "auto"
 
 [tool.ruff.lint]
 select = [
-    "E",   # pycodestyle errors
-    "W",   # pycodestyle warnings
-    "F",   # pyflakes
-    "I",   # isort
-    "B",   # flake8-bugbear
-    "C4",  # flake8-comprehensions
-    "UP",  # pyupgrade
+    "E",  # pycodestyle errors
+    "W",  # pycodestyle warnings
+    "F",  # pyflakes
+    "I",  # isort
+    "B",  # flake8-bugbear
+    "C4", # flake8-comprehensions
+    "UP", # pyupgrade
 ]
 ignore = [
-    "E501",  # line too long (handled by formatter)
-    "B008",  # do not perform function calls in argument defaults
+    "E501", # line too long (handled by formatter)
+    "B008", # do not perform function calls in argument defaults
 ]
 
 [tool.ruff.lint.isort]
 known-first-party = ["genmetaballs"]
 [tool.pixi.activation.env]
-PYOPENGL_PLATFORM = "osmesa"
+PYOPENGL_PLATFORM = "osmesa"