Update RankingTrainer usage and Remove BLAS

[OctoberChang]

Issue #, if available:

Description of changes:

• Slight adjustment of RankingTrainer class to support custom loss functions for its child-class
• Remove dependency of BLAS, so the package is more lightweight
• Bump minimal support Python version from 3.8 to 3.9 (Py3.8 is end-of-life as of 2024/10/07)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.