[RFC] add class support in bc-linter

[zhewenl]

as discussed with @izaitsevfb, we want to also include linter checks on classes in addition to public functions; but prior to landing this PR, we need to create some rules template for linters, where we can define what to check(or not).
Like:

pytorch:
- Files: global
- Include: functions

vLLM:
- Files: vllm/v1/attrition, vllm/v1/core
- Include, classes, functions

cc @huydhn @yangw-dev @houseroad

[vercel]

@zhewenl is attempting to deploy a commit to the Meta Open Source Team on Vercel.

A member of the Team first needs to authorize it.

[izaitsevfb]

Ran the new version retroactively on the recent PyTorch history (4000 commits).

Raw findings:

- e65ab9a868aff9397a695085b3f8a2199724771c vs bfe6765d6b621f60e3dfd6d891d0177bc1
5d5e6c
  - File: torchgen/gen_aoti_c_shim.py
  - Violation: FieldTypeChanged in class ShimGenerator, field dispatch_key
  - Diff: Shows typing import and generator changes; type of a dataclass field a
ppears to have changed.
  - PR: 158974
  - Labels: includes suppress-bc-linter

- 02ca965560e74e44dfd446d97b77d84eb35b2de2 vs 511d9873789b11e7c84fcfdfffa9166faa
0d83b3
  - File: torch/distributed/checkpoint/staging.py
  - Violation: FieldRemoved in class StagingOptions, field use_cuda_non_blocking
_copy (renamed to use_non_blocking_copy)
  - Diff: Renames option name; our linter sees it as removal.
  - PR: 158337
  - Labels: no suppress-bc-linter label

- f76f4abf3f10bd36a47e7cebdce90290ce76e564 vs be483a54817fbfbf184af363bf9469d01b
fa15ef
  - File: tools/stats/monitor.py
  - Violations: FieldAdded x3 in class GpuData (allocated_mem, allocated_mem_val
ue, total_mem_value)
  - Diff: Adds three dataclass fields with no defaults; our policy flags require
d dataclass field additions.
  - PR: 156907
  - Labels: no suppress-bc-linter label
  - Note: This is outside core library (tools/), but still detected.

- 250ae2531c55dcc50f558ec739941324e3f9a4d4 vs 011026205a9d4c38458130f8ca242028f6
184bf0
  - File: torch/cuda/graphs.py
  - Violation: FieldTypeChanged in class graph, field default_capture_stream
  - Diff: Large typing cleanup; type for the field likely changed.
  - PR: 158192
  - Labels: no suppress-bc-linter label (topic: not user facing)

- 4283d96bcdf9aaa4289985267186d74ba6534ee5 vs b4476ca378be50034bd5cdc1eaa9510433
7c998a
  - File: setup.py
  - Violation: ClassDeleted for wheel_concatenate (build-time class removed)
  - Diff: Removes external wheel.bdist_wheel shim usage.
  - PR: 157783
  - Labels: includes suppress-bc-linter

Some observations:

• not many class violations in PyTorch codebase.
• reported violations are on-point (though some are on internal surface)
• no noticeable regression in bc-linter behavior