refactor(table): remove orphan cleanup walk fallback

[Herrtian]

Summary

• Remove the unreachable LocalFS/blob fallback from orphan cleanup walkDirectory
• Return an explicit error if a future IO implementation does not implement ListableIO
• Add a regression test for that defensive error

Fixes #1276.

Tests

• go test ./table -run TestWalkDirectoryRequiresListableIO -count=1

I also tried the broader orphan-cleanup subset on Windows; it currently fails in existing path-normalization tests that expect S3 URL paths with / while Windows produces escaped backslashes (%5C).

[Herrtian]

Closing this draft.