Switch from pybind11 to nanobind

[inducer]

Surprisingly, this is mostly working now. :)

To do/Needs:

• [x] ~~Pass location of numpy headers to CMake~~ (found via CMake now)
• [x] ~~Pass OpenCL config info to CMake~~ (found via CMake now)
• [x] Actually fix the wrapper :slightly_smiling_face:
  • [x] pycl test_wrapper.py 'test_mempool(cl._csc)' crashes
  • [x] PYOPENCL_TEST=port python test_array.py "test_mem_pool_with_arrays(cl._csc)" crashes
  • [x] Doesn't make it through the meshmode test suite
• [x] https://github.com/wjakob/nanobind/pull/38
• [x] ~~https://github.com/wjakob/nanobind/pull/23~~
• [x] ~~https://github.com/wjakob/nanobind/pull/24~~
• [x] ~~See if the _enqueue trampoline can be avoided~~ (doesn't matter for loopy enqueues, that goes straight to enqueue_nd_range_kernel)
• [x] ~~https://github.com/wjakob/nanobind/pull/71~~
• [ ] Expose SVM-as-buffer
• [ ] Investigate reference leaks after tests
• [ ] Pass CI
• [ ] Check loopy CI. Currently, it requires weak references to cl.Context, which nanobind doesn't currently allow.
• [ ] Work around https://github.com/wjakob/nanobind/pull/72

[inducer]

The infinite recursions appear to be https://github.com/wjakob/nanobind/pull/72.