Improve Memory Usage Efficiency and Other Miscellaneous

Improve Memory Usage Efficiency

[x] Change grid_levels from NPY_LONG to NPY_INT. (allocate_hierarchy.cpp, append_grid.cpp)

Always wrap data passed in, and we can look up data info using NumPy API, instead of searching in libyt yt_grid array.
[x] Make yt_getGridInfo_* look up in libyt Python module.
- I should use this, otherwise we are always searching gid in local grids array.
[x] Return data buffer from libyt Python module in yt_getGridInfo_FieldData.
- Something like PyArray_DATA, PyArray_DIMS, PyArray_DESCR
[x] Dealing with particle_count_list: load each ptype separately, and then sum them up in libyt frontend.
- [x] Loading particle. (allocate_hierarchy.cpp, append_grid.cpp)
- [x] Create grid_particle_count through frontend. (data_structures.py, yt_commit.cpp, )
- [x] Look up API.
- [x] Get each ptype number through ptype number array, and determine do they need RMA process.
[x] Add prototype to libyt.h.
[x] Make sure every search uses this look up API.
[x] Check RMA process.
[x] Clean up: delete unused resource.
[x] Check setting data dimension in append_grid.cpp. Do I need this?
[x] Remember to free grids_local under g_param_yt, once yt_commit is done.
[ ] Update paper section 2.6.

Always wrap data pass in
When passing data to Python
- [x] Do not create key-value pair if no field data pointer to wrap when creating libyt.grid_data.
- [x] Check RMA process, don't create key-value pair if some data did not found on some rank.
- It looks like I did this already...
When passing hierarchy to Python
- Make Python stores one copy of full hierarchy only.
- [x] Assign libyt's hierarchy directly in yt.
  - Override _initialize_grid_arrays
  - Rewrite abstract _parse_index
- [x] Reexamine libyt's hierarchy new allocated buffer.
- [x] Reexamine particle count data type.
  - Stay with long, since we now assign libyt allocated array in yt frontend.

[x] Make MPI_Datatype yt_hierarchy_mpi_type initialize once only. (yt_commit_grids.cpp)
[x] Make MPI_Datatype yt_rma_grid_info_mpi_type initialize once only. (yt_rma_field.cpp)
[x] Make MPI_Datatype yt_rma_particle_info_mpi_type initialize once only. (yt_rma_particle.cpp)
[x] Make GitHub Action generate data through code, not directly store data in txt file.
[x] Make example more simple.
[x] Make INFO log only print in root rank.
[x] Mark in-memory field data read-only API when wrapping data array.
- https://numpy.org/devdocs/reference/c-api/array.html#c.NPY_ARRAY_WRITEABLE
[ ] #62
[x] Change user guide overview to a list of libyt API.
[x] YT_ERROR: you want to implement your new yt_dtype, you should modify both yt_dtype Enum and get_npy_dtype function.
- Caused by if get_dtype_property cannot get NumPy data type, it prints error log.
- libyt first look through data_dtype then field_dtype, it is ok if data_dtype is not set.
[x] Make general info like MyRank and MySize global.
[x] Use function templates in big_mpi.cpp (not feasible, have to declare every time we used it.)
[ ] Don't do copy when using append_grid.cpp

[x] Reexamine no_locks, do I even need that.
- https://wgropp.cs.illinois.edu/courses/cs598-s15/lectures/lecture35.pdf
- https://cvw.cac.cornell.edu/mpionesided/fence
- Will schedule point-to-point communication faster than RMA? (Just curious).