chore(host): Refactor fetchers

[clabby]

Overview

Refactors the fetchers for the single and interop host modes into a shared type, where hint handling can be customized via the HintHandler trait.

makes progress on #987, but doesn't yet implement support on the client side.

[clabby]

📚 $\text{Stack Overview}$

Pulls submitted in this stack:

• chore(host): Refactor fetchers #995 👈
• chore(host): Remove HostOrchestrator #994
• main

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 89.0%. Comparing base (6ca5552) to head (8d7067c).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/proof-sdk/preimage/src/key.rs	0.0%	13 Missing ⚠️

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[refcell]

I actually like the hint handler abstraction, think it works fairly clean. Can always improve later on