feat(client): Wire up L2PayloadWitness hint for single-chain proof

[clabby]

Overview

Experimental wiring of the L2PayloadWitness hint, allowing op-reth to be used as the backing L2 execution client for kona-host.

[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 12 lines in your changes missing coverage. Please review.

Project coverage is 85.6%. Comparing base (b31d080) to head (a5e80cd).
Report is 7 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/proof/mpt/src/noop.rs	0.0%	7 Missing ⚠️
bin/host/src/single/handler.rs	40.0%	3 Missing ⚠️
crates/proof/proof-interop/src/hint.rs	0.0%	2 Missing ⚠️

Additional details and impacted files

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[refcell]

Codecov hurts me soul

wen monorepo we will need to be stricter about this...