Import the open_source branch of NKIPyKernelGen into `kernelgen/` as a
self-contained subpackage. NKIPyKernelGen is a compiler that traces NumPy
functions and lowers them to NISA (Neuron Instruction Set Architecture)
for AWS Neuron hardware. Users write kernels in Python with `@trace` and
`knob.knob()` annotations; the compiler handles tiling, memory placement,
layout legalization, and NISA lowering.

What's included
---------------
- `kernelgen/nkipy_kernelgen/`  — Python tracing frontend:
    - `trace.py` (@trace decorator)
    - `knob.py` (tensor annotations: mem_space, tile_size, reduction_tile,
      partition_dim)
    - `traced_array.py` (TracedArray wrapping MLIR SSA values)
    - `op_vtable.py` (NumPy op → MLIR lowering table)
    - `transforms/nkipy_opt.py` (pipeline orchestration, shells out to
      `nkipy-opt`)
- `kernelgen/mlir/`             — MLIR dialect + C++ passes:
    - `nkipy.annotate` op (target, mem_space, partition_dim, tile_size,
      reduction_tile)
    - 20+ transformation passes under `mlir/lib/Transforms/` implementing
      the 24-pass compilation pipeline (InferLayout, KnobDrivenTiling,
      AnnotateMemorySpace, LegalizeLayout, InsertSpillReload,
      LinalgToNisa, etc.)
- `kernelgen/tests/`            — test suite:
    - `passes/` — per-pass FileCheck tests
    - `e2e/`    — end-to-end tests (trace → NISA → BIR sim / HW)
    - `unit/`   — Python-level unit tests
    - `harness.py` — unified test harness with LLVM/BIR_SIM/HW/FileCheck
      modes
- `kernelgen/examples/`         — example kernels
- `kernelgen/compiler_explorer/` — Compiler Explorer wrapper for inspecting
  IR at any pipeline stage
- `kernelgen/setup.py`, `pyproject.toml`, `pytest.ini`, `requirements.txt`
  — build + test configuration (`pip install -e kernelgen/` builds the
  C++ passes via CMake)
- `kernelgen/CLAUDE.md`, `README.md` — pipeline docs and usage notes

Architecture notes
------------------
NKIPyKernelGen depends on the NISA dialect defined in private-nki-staging
(the `nki` wheel). NKIPyKernelGen's `nkipy-opt` binary performs the
tensor-level and bufferization phases; lowering to BIR then runs through
the upstream `nki-opt-pipeline`. This import does not bring in the NISA
dialect sources — only NKIPyKernelGen's own passes and frontend.

Ignore rules
------------
Added a `!mlir/lib/` override in `kernelgen/.gitignore` so the parent
nkipy repo's `lib/` rule (intended for Python venv `lib/` dirs) does not
silently exclude the MLIR C++ pass sources under `kernelgen/mlir/lib/`.

Source
------
Imported from NKIPyKernelGen `open_source` branch @ commit 973c1be
("fix: correct mem_space enum values in builder.annotate()"). Internal
git history is not preserved — this is a single squash import for the
open-source release.