Megfile

- fix
- fix `pickle.load` `S3UnknownError` bug

- **breaking change**
- Remove the `followlinks` parameter from `hdfs_listdir`, `hdfs_load_from`, `hdfs_scandir`, `HdfsPath.load`, `HdfsPath.scandir`, and keep the behavior as `followlinks=False`.
- Remove the `followlinks` parameter from `s3_access`, `s3_listdir`, `s3_load_from`, `s3_scandir`, `s3_glob`, `s3_glob_stat`, `s3_iglob`, `s3_load_content`, `S3Path.access`, `S3Path.listdir`, `S3Path.load`, `S3Path.scandir`, `S3Path.glob`, `S3Path.glob_stat`, `S3Path.iglob`, `S3Path.iterdir`, and keep the behavior as `followlinks=False`.
- Remove the `missing_ok` parameter from `s3_listdir`, `s3_scandir`, `S3Path.listdir`, `S3Path.scandir`, and set the default behavior to `missing_ok=False`.
- `Path.iterdir` and `Path.scandir` no longer guarantees dictionary order. If order is required, please use `Path.listdir`.
- perf
- reduce the use of `is_dir` in S3 to decrease the number of requests
- fix
- Fix `is_symlink` in the `StatResult` returned by `S3Path.scandir` is incorrect.
- Fix `SftpPath.listdir` throwing an error when the input is a symbolic link.
- Fix an issue that `S3PermissionError` is raised when performing a `mkdir` operation without sufficient permissions on S3.

- perf
- reduce the use of `is_dir` in S3 to decrease the number of requests

- perf
- keep reading file even if etag is not returned from s3 server

- feat
- add env `MEGFILE_LOG_LEVEL` for set log level
- add `--log-level` in cli for set log level
- fix
- fix `max_buffer_size` not work when is `0` in `smart_open`

- feat
- support kubernetes canonical form quantity in environment variable
- support add host key for sftp
- perf
- use `head_object` to get file size in prefetch reader when no cache
- fix
- fix `smart_load_content` bug when only end is not None