[math] Replace math operators with braintaichi

[Routhleck]

This pull request introduces support for the braintaichi library in addition to the existing taichi library. It includes changes to dependency checks, updates to the deep neural network (DNN) linear module, and modifications to various test files to accommodate the new library.

Dependency Check Updates:

• Added import_braintaichi and raise_braintaichi_not_found functions to brainpy/_src/dependency_check.py and updated the minimal version for taichi. [1] [2] [3] [4]

DNN Linear Module Updates:

• Imported braintaichi and updated the dense_on_post, dense_on_pre, csr_on_pre_update, coo_on_pre_update, coo_on_post_update, and csc_on_post_update functions to use braintaichi.XLACustomOp instead of bm.XLACustomOp if braintaichi is available. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Test File Updates:

• Removed import_taichi and the corresponding pytest.skip calls from various test files, and updated tests to use jax.numpy as jnp. [1] [2] [3] [4] [5] [6] [7] [8]

Other Changes:

• Removed the import of tifunc from brainpy/_src/math/__init__.py.
• Updated csr_matmat.py to use braintaichi and removed unused imports.

[chaoming0625]

Great work.