test: loading assumeutxo snapshot start states

[BrandonOdiwuor]

Fixes: #28648

Add assumeutxo test:

• loading snapshot with current chain tip at snapshot_base_height
• loading snapshot with current chain tip a descendant of snapshot block

[DrahtBot]

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #29996 (test: Assumeutxo: import snapshot in a node with a divergent chain by alfonsoromanz)
• #29553 (assumeutxo: Add dumptxoutset height param, remove shell scripts by fjahr)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[DrahtBot]

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_{Debug: https://github.com/bitcoin/bitcoin/runs/23007390361}

[maflcko]

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