fix(providers): Remove Slot Derivation

[refcell]

Description

Removes the SlotDerivation trait and inlines the SimpleSlotDerivation method into the OnlineBlobProvider. If it becomes needed elsewhere, we can refactor down the road to pull it out of the OnlineBlobProvider into it's own type without specifying it as a generic.

Metadata

Closes #632

[codecov]

Codecov Report

Attention: Patch coverage is 90.62500% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.0%. Comparing base (ed6c0db) to head (1ead1dc).
Report is 2 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/providers-alloy/src/blob_provider.rs	90.3%	3 Missing ⚠️

Additional details and impacted files

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