fix(derive): Holocene SpanBatch prefix checks

[clabby]

Overview

Fixes the Holocene span batch prefix checks by using the l1 inclusion timestamp over the batch timestamp. This matters because first channel after Holocene may have some batches pre-Holocene and some batches after. h/t @sebastianst

think about the first channel after Holocene activation. Its first batches will have a batch timestamp pre-Holocene, so the new rules wouldn't be applied to those, and worst case the validation would return e.g. a BatchFuture validity, which gets removed with Holocene. So I'm afraid we do have to activate those rules by l1 inclusion block timestamp.

Also, de-duplicates some code by re-using the check_batch_prefix function in SpanBatch::check_batch.

[codecov]

Codecov Report

Attention: Patch coverage is 96.22642% with 4 lines in your changes missing coverage. Please review.

Project coverage is 94.0%. Comparing base (38cf22e) to head (04b933c).
Report is 3 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/derive/src/batch/span_batch/batch.rs	95.1%	4 Missing ⚠️

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