[CI] Refactor the CI to be more modular and user-friendly

Only run the latest commit of the user's PR.
Split unit tests by folder and functional tests by model into different jobs to avoid repeated runs when tests fail.
Use YAML files to control the content of unit and functional tests.
Before running the pytest command each time, check if the GPU is idle to avoid test failures caused by resource contention.

tests/scripts/unit_tests/test_all.sh

tests/scripts/unit_tests/test_subset.sh --backend megatron --subset transformer

Without adding a new folder:
- No modification needed.
When adding a new folder:
- Modify the tests/scripts/unit_tests/config.yml configuration file.
Configuration file structure
- Framework name(megatron/flagscale/...):
  - set_environment: Commands to configure the environment.
  - coverage: Directories that require test coverage statistics (the actual path = framework name + directory name).
- Subset name(models/transformer/...):
  - depth: Specify which levels of tests to run. Default is to run all (all), also can be a integer.
  - ignore: Specify folders, files, or functions to skip.
  - type: Batch test or independent test. Default is batch (batch), also can be (single).
Note: Default values do not need to be explicitly marked. If a folder uses all default configurations, it can be omitted from the configuration file. Here is an example of adding your own testing folder.
```
flagscale:
  subset:
    your_folder:
      type: batch 
      depth: all 
      ignore: pytest_file.py
```
How to run this example
```
tests/scripts/unit_tests/test_subset.sh --backend flagscale --subset your_folder
```

FlagOpen / FlagScale