feat(mpt): Migrate to thiserror

[clabby]

Overview

Migrates kona-mpt to typed errors.

[codecov]

Codecov Report

Attention: Patch coverage is 74.52830% with 27 lines in your changes missing coverage. Please review.

Project coverage is 78.1%. Comparing base (72908f9) to head (b22b96b).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/mpt/src/node.rs	58.3%	15 Missing ⚠️
crates/mpt/src/db/mod.rs	81.8%	4 Missing ⚠️
crates/mpt/src/errors.rs	0.0%	3 Missing ⚠️
crates/mpt/src/fetcher.rs	72.7%	3 Missing ⚠️
crates/mpt/src/list_walker.rs	89.4%	2 Missing ⚠️

Additional details and impacted files

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