refactor model weights, utils for yoloworld variants to follow the new naming convention

[ashokkumarkannan1]

Problem description

• Model variant names were updated to follow the new naming convention introduced in this PR:
  Update model names to human-readable format for presentation (#447) #472

• However, this change breaks existing model loading because:
  a) Model weights stored in S3 are resolved using the variant name - s3://tt-ci-models-private/test_files/pytorch/yoloworld/
  b) Configuration loading logic also depends on the variant name.

As a result, renaming the variants without updating corresponding assets and references causes weight resolution and config loading failures.

What’s Changed

• Refactored utilities and loader logic to align with the updated variant naming convention.
• Renamed the weight files for all YOLOWorld variants in S3 to match the new naming scheme.

Checklist

• New/Existing tests provide coverage for changes

Logs

• xlarge_640.log
• large_640.log
• large_1280.log
• medium_640.log
• medium_1280.log
• small_640.log
• small_1280.log