Change the default value of the `timeout` parameter from 300 to None
for all HTTP request methods (get, post, put, delete, post_bytesio,
and download_file) in the request module. This allows the requests
to use the system's default timeout behavior when no explicit timeout
is provided, improving flexibility and alignment with standard practices.

- Introduce new `all_catalog_names()` function in catalog.py to fetch available catalog names
- Enhance `is_valid_datetime_format()` to accept both basic and ISO datetime formats
- Add corresponding unit test for `all_catalog_names()`
- Comment out slow integration tests in level0/level1 test files

- Remove unused return type annotation in post_file function
- Update find functions in level0 and level1 modules to require instrument parameter