feat: support nest log

[Zeyi-Lin]

Description

This pull request includes changes to the swanlab/data/run/main.py file to add support for logging nested dictionaries by flattening them. The most important changes include adding a helper method to flatten nested dictionaries, updating the log method to handle nested dictionaries, and modifying the key format check to work with the flattened dictionary.

Improvements to nested dictionary handling:

• swanlab/data/run/main.py: Added a helper method __flatten_dict to flatten nested dictionaries with dot notation.
• swanlab/data/run/main.py: Updated the log method to accept nested dictionaries and flatten them before processing. [1] [2]

Closes: #806

使用案例：

import swanlab

swanlab.init(project="dev")

data = {'a': {'b': {'c': 1, 'd': 2}, 'e': 3}, 'f': 4}
swanlab.log(data)