feat(node): use postage snapshot on --resync unless skipped

[gacevicljubisa]

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Description

--resync on an existing batch store rescanned the whole postage contract from the chain, because the snapshot only loaded when no store existed. Since a resync wipes the store anyway, treat it as "no store" and rebuild from the embedded snapshot on --resync too, unless --skip-postage-snapshot is set.

Decision extracted into useEmbeddedSnapshot with a table test.

Open API Spec Version Changes (if applicable)

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