refactor(reexecute/c): export CreateBlockChanFromLevelDB

[RodrigoVillar]

Why this should be merged

As part of switching from using go bench to custom benchmarks in the reexecution tests (#4508), we'll need to export CreateBlockChanFromLevelDB() so that the reexecution test and the export block range tool can use this (as they'll be living in separate packages as executables).

This PR is a precursor to #4639.

How this works

Moves CreateBlockChanFromLevelDB() and BlockKey() to the reexecute package so that it's accessible to both the reexecution test and the export block range test.

How this was tested

CI + ran task export-cchain-block-range locally

Need to be documented in RELEASES.md?

No

[Copilot]

Pull request overview

This PR refactors the reexecution test utilities by moving CreateBlockChanFromLevelDB() and BlockKey() functions from the tests/reexecute/c package to the new tests/reexecute package, making them publicly accessible for reuse across multiple packages.

Key changes:

• Created new tests/reexecute/db.go file with exported CreateBlockChanFromLevelDB() and BlockKey() functions
• Updated tests/reexecute/c/vm_reexecute_test.go to use the newly exported functions from the reexecute package
• Removed duplicate code by consolidating shared functionality into a single, reusable location

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/reexecute/db.go	New file containing exported block database utilities with CreateBlockChanFromLevelDB(), BlockKey(), and BlockResult type
tests/reexecute/c/vm_reexecute_test.go	Updated to import and use the refactored functions from the reexecute package, removing local implementations

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