Check block height before populating BlockCache (#1388)

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## Overview
Duplicate of #1381 but merges to
main.

Also, closes: #1387

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## Checklist

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

- **Refactor**
- Improved the block processing logic to ensure blocks are only
processed if they are new or unprocessed, enhancing the efficiency and
reliability of the system.

- **Bug Fixes**
- Addressed an issue where previously processed blocks could be
processed again, potentially leading to inconsistencies.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: gupadhyaya

block/manager.go

@@ -306,6 +306,7 @@ func (m *Manager) SyncLoop(ctx context.Context, cancel context.CancelFunc) {
 		case <-blockTicker.C:
 			m.sendNonBlockingSignalToBlockStoreCh()
 		case blockEvent := <-m.blockInCh:
+			// Only validated blocks are sent to blockInCh, so we can safely assume that blockEvent.block is valid
 			block := blockEvent.block
 			daHeight := blockEvent.daHeight
 			blockHash := block.Hash().String()
@@ -315,7 +316,7 @@ func (m *Manager) SyncLoop(ctx context.Context, cancel context.CancelFunc) {
 				"daHeight", daHeight,
 				"hash", blockHash,
 			)
-			if m.blockCache.isSeen(blockHash) {
+			if blockHeight <= m.store.Height() || m.blockCache.isSeen(blockHash) {
 				m.logger.Debug("block already seen", "height", blockHeight, "block hash", blockHash)
 				continue
 			}