Cache RootLists with KVCachedFile

[ihtefyw]

The RootList in the MPT archive implementation keeps all the root hashes in memory and can grow indefinitely.
Similarly to #434, this PR adds a caching layer to RootList by using the KVCachedFile.
A new KVFile called OrderedFile is added, an array-like storage with a key-file offset mapping.

Closes https://github.com/0xsoniclabs/sonic-admin/issues/845

[Copilot]

Pull request overview

This PR introduces a disk-backed caching layer for the MPT archive RootList using common.KVCachedFile to prevent unbounded in-memory growth, and adds migration logic to convert the legacy roots.dat format into the new key+value format.

Changes:

• Add a new root_list.go implementing rootList on top of KVCachedFile with a versioned header + legacy migration.
• Update ArchiveTrie to use the new rootList API (error-returning Get/Append) and adjust verification to read roots via GetAll.
• Add comprehensive tests for root list persistence, migration, and checkpoint/restore behavior; update archive trie tests accordingly.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 10 comments.

File	Description
go/database/mpt/root_list.go	New KVCachedFile-backed root list, including on-disk format/versioning and migration + restore/truncate helpers.
go/database/mpt/root_list_test.go	New/ported tests covering header/version, read/write roundtrips, migration, checkpoint integration, and truncate/restore flows.
go/database/mpt/archive_trie.go	Switch archive trie root handling to the new rootList methods and update verification/root access paths.
go/database/mpt/archive_trie_test.go	Update tests to construct a real rootList and remove tests tied to the old in-memory slice behavior.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

[codecov]

Codecov Report

❌ Patch coverage is 60.13986% with 57 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
go/database/mpt/archive_trie.go	56.81%	36 Missing and 21 partials ⚠️

❌ Your patch check has failed because the patch coverage (60.13%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Files with missing lines	Coverage Δ
go/database/mpt/live_trie.go	98.40% <100.00%> (-1.60%)	⬇️
go/database/mpt/verification.go	83.33% <100.00%> (+0.16%)	⬆️
go/database/mpt/archive_trie.go	87.88% <56.81%> (-10.35%)	⬇️

... and 2 files with indirect coverage changes

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