kernel-builder: move build.toml parsing to kernels-data

[danieldk]

This change moves over parse_and_validate to kernels-data and exposes it as Build::open. We also make this function available through the Python API as well as a small number of methods from Build.

The Build methods that are made available through the Python API are guided by what is needed for dependency support. In general, we do not want to do any build.toml parsing in kernels, since it's a build-side file format. However, to be able to build a kernel with dependencies in Nix, we need to lock the dependencies and this is the same locking code as used by kernels lock. The only difference is that we take the kernels from build.toml and not pyproject.toml. For this reason, exposing build.toml to the client in a minor way seems justified for this specific purpose.

[sayakpaul]

Nice!

[sayakpaul]

Thanks. Just one question regarding adding a test.

[github-actions]

Coverage report — kernels/

Measured on: Python 3.10 / Torch 2.13.0.
Other CI configurations are not included in this number.
Hardware-gated code paths (ROCm/XPU/NPU/Darwin/Windows) are excluded or unreachable on the Linux+CUDA runner.

Total coverage: 84.3% — threshold: 80% — ✅

Per-file breakdown

Name	Stmts	Miss	Cover	Missing
src/kernels/__init__.py	13	0	100%
src/kernels/_system.py	6	1	83%	10
src/kernels/_versions.py	63	7	89%	46, 49, 52-53, 56-57, 100
src/kernels/backends.py	212	62	71%	40, 44, 48-51, 68, 90, 108, 117, 121, 125-127, 148, 157, 161, 165-167, 188, 199, 201, 208-211, 224, 228, 232-252, 260, 283-303
src/kernels/compat.py	8	1	88%	5
src/kernels/deps.py	58	4	93%	59-60, 101, 104
src/kernels/hf_hub.py	62	5	92%	18, 20, 114, 136-137
src/kernels/importer.py	48	3	94%	106, 110, 113
src/kernels/install.py	50	5	90%	78, 116-117, 155, 173
src/kernels/layer/__init__.py	6	0	100%
src/kernels/layer/_interval_tree.py	103	4	96%	23, 52, 147, 150
src/kernels/layer/device.py	48	14	71%	42, 47-49, 91, 96-98, 101, 149, 152, 155-157
src/kernels/layer/func.py	82	7	91%	83, 113, 185, 303, 309, 322, 340
src/kernels/layer/globals.py	5	0	100%
src/kernels/layer/kernelize.py	74	8	89%	255, 281, 289-290, 296, 300, 316-318
src/kernels/layer/layer.py	211	16	92%	169, 212, 218, 231, 339, 419-420, 432, 441, 449, 460, 489, 493, 506, 559, 589
src/kernels/layer/mode.py	14	0	100%
src/kernels/layer/repos.py	144	42	71%	27, 33, 36-43, 63-64, 70, 73-76, 90, 94, 103-104, 110, 113-116, 123-124, 130, 133-136, 143-144, 150, 153-156, 163-164, 170, 173-176, 257
src/kernels/load.py	74	9	88%	218, 224, 230-231, 252-264
src/kernels/locking.py	108	70	35%	42-109, 113-136, 144, 148-155, 159-169, 173-180
src/kernels/status.py	49	2	96%	23, 81
src/kernels/variants.py	278	22	92%	64, 95, 116, 146, 255-256, 298-301, 303, 387-394, 400-406, 437-443, 455-461, 611-613
src/kernels/verify.py	88	1	99%	32
TOTAL	1804	283	84%

Updated by the Test kernels workflow on commit e38cc32c4206fa2e69e159902dbecae7a9e99fc9.

[sayakpaul]

Great!