fix(postage): resume live sync where snapshot replay stopped

[gacevicljubisa]

Checklist

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• I have added tests to cover my changes.
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Description

Follow-up to #5499. When booting from the postage snapshot, the snapshot replay
stops a few blocks below the snapshot's max block (the listener trims tailSize
and rounds to a batchFactor multiple). But live sync was forced to resume from
the snapshot's nominal tip (maxBlock + 1) via snapshotResumeBlock, skipping
those few blocks. A BatchCreated in that gap later surfaces as
get batch <id>: storage: not found.

Fix: drop the snapshotResumeBlock override. Start already resumes from
cs.Block + 1, and the replay advances cs.Block as it goes, so live sync now
resumes exactly where the replay stopped and re-fetches the trimmed tail from the
chain. No events skipped, none double-processed.

• pkg/postage/batchservice: remove snapshotResumeBlock and the Start
  override; remove ResumeBlock from the Snapshot struct.
• pkg/postage/snapshot: New still parses the snapshot eagerly (corruption
  guard), but no longer carries a resume block.
• Tests: TestSnapshotRebuild asserts live resumes from the replay's last block;
  TestReplayStopsBelowMaxBlock (real listener + filterer) asserts the replay
  stops below maxBlock; restored TestSnapshotLogFilterer_RealSnapshot (dropped
  by the chore: revert #5343 #5482 revert) parses the embedded blob and asserts it is non-empty.

Open API Spec Version Changes (if applicable)

Motivation and Context (Optional)

Related Issue (Optional)

Related to #5495, follow-up to #5499. Restores a real-archive test removed by the
#5343 revert (#5482).

Screenshots (if appropriate):

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[gacevicljubisa]

Here is the failing test @acud and @martinconic
https://github.com/ethersphere/bee/actions/runs/28029337125/job/82965450122?pr=5518#step:8:95

On current branch, you can find this test in pkg/postage/batchservice/batchservice_test.go with the name TestSnapshotHandoffNoGap, where it passes.

[acud]

lgtm. nice catch