Add smart parallel downloads

[ghimiresdp]

Description

Until now, we could pass number of threads for files of any size, but for files that are sufficiently smaller (example: files less than 1 MB), single thread will be used to download resources.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement

Checklist

• I have run cargo fmt to ensure consistent code style.
• I have run cargo test and all tests passed.
• I have added new tests that prove my fix is effective or that my feature works.
• I have updated the README.md (if applicable).

Performance Impact