Decouple Delta path discovery from Bucket

[kaklakariada]

Review follow-up from PR #394 for issue #393.

The generic Bucket abstraction currently knows about DeltaLog and decides how to enumerate Delta paths internally. This mixes storage path access with Delta table interpretation.

Proposed direction:

• Move Delta-specific path discovery behind a dedicated collaborator.
• Inject path discovery into the code that needs it instead of letting Bucket know DeltaLog details.
• Keep Bucket responsible for storage configuration and filesystem access only.