compatible with brainstate>=0.1.0

[chaoming0625]

This pull request includes several changes to the braintools project, focusing on adding new functionality, updating dependencies, and improving code consistency. The most important changes include the addition of a new spike encoder, updates to licensing information, and modifications to dependency requirements.

New Functionality:

• Added LatencyEncoder class in braintools/_others/spike_encoder.py to encode rate input as spike trains using latency encoding.

Licensing Updates:

• Added Apache License headers to braintools/_others/__init__.py and braintools/_others/spike_encoder.py. [1] [2]

Dependency Updates:

• Updated pyproject.toml and setup.py to specify a minimum version for the brainstate package. [1] [2]

Code Improvements:

• Changed bst.transform.for_loop to bst.compile.for_loop in multiple files for improved performance. [1] [2] [3]
• Modified the msgpack_save function in braintools/file/msg_checkpoint.py to remove unnecessary file extension checks.

Import and All Updates:

• Updated __init__.py files to include new imports and adjust the __all__ variable for proper module exports. [1] [2]