[tools] add utilities for deterministic port to kernels

[sayakpaul]

Related to #729.

I know we have been talking about having a new DSL. I didn't take that route in this PR. Instead, I decided to add atomic components that can be used in isolation as well as in the DSL. These operations include:

• Determining the latest release tag and then fetching it for a given kernel repository on GitHub.
• Relativizing imports as specified in https://huggingface.co/docs/kernels/main/en/kernel-requirements
• Fixing PyTorch op registration as specified in https://huggingface.co/docs/kernels/main/en/kernel-requirements through ASTs

Have added tests for each atomic operation, too. But didn't intentionally add them to the CI because we still haven't decided on the direction this whole utility would take.

Tip

I think for the initial review, it's more important to decide if we want to have this kind of atomic utilities and agree on their signatures rather than their actual implementation details. Best to maybe start with the README.md added in this PR to get a sense of how I have decided to structure it.

TODOs:

• Documentation. Planning on having either a short section or an entire page dedicated to "porting existing kernel projects to be kernel-builder compliant".
• Wire this up in AGENTS.md of kernels-community so that agents actually know which tools to use for deriving deterministic outputs rather than hits and misses.

[github-actions]

Coverage report — kernels/

Measured on: Python 3.10 / Torch 2.12.0.
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: 84.6% — threshold: 80% — ✅

Per-file breakdown

Name	Stmts	Miss	Cover	Missing
src/kernels/__init__.py	10	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	194	55	72%	40, 44, 48-51, 68, 90, 108, 117, 121, 125-127, 148, 170, 181, 188-191, 201, 205-225, 233, 256-276
src/kernels/compat.py	8	1	88%	5
src/kernels/deps.py	54	4	93%	58-59, 95, 98
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	81	7	91%	81, 111, 183, 301, 307, 320, 338
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	210	16	92%	167, 210, 216, 229, 337, 417-418, 430, 439, 447, 458, 487, 491, 504, 557, 587
src/kernels/layer/mode.py	14	0	100%
src/kernels/layer/repos.py	130	34	74%	27, 33, 36-41, 61-62, 68, 71-74, 88, 92, 101-102, 108, 111-114, 121-122, 128, 131-134, 141-142, 148, 151-154, 235
src/kernels/lockfile.py	71	46	35%	37-104, 108-131
src/kernels/status.py	49	2	96%	23, 81
src/kernels/utils.py	313	55	82%	65, 77-81, 87-88, 246, 250, 253, 315, 323, 362-363, 401, 432, 437, 472, 701, 704, 706, 712, 725-726, 747-759, 763-770, 778, 782-792, 796-803, 841, 845, 864, 866
src/kernels/variants.py	270	22	92%	63, 94, 115, 145, 254-255, 297-300, 302, 386-393, 399-405, 436-442, 454-460, 559-561
src/kernels/verify.py	88	1	99%	32
TOTAL	1797	277	85%

Updated by the Test kernels workflow on commit 1c3ffcbdae46329530fa26cae16f0ad424c38fa2.