refactor(core): use errors.Is for sentinel error comparisons in blockchain.go

[gzliudan]

Description

Replace direct == / != comparisons against sentinel errors in core/blockchain.go with errors.Is, matching modern Go idiom (used elsewhere in this file, e.g. errors.Is(err, ErrGenesisAllocUnavailable)).

errors.Is is behaviorally identical for these plain errors.New sentinels today, but also matches wrapped errors (fmt.Errorf("...: %w", err)), so future refactors that wrap these sentinels won't silently break insertion-path error handling.

Changes

11 comparisons updated:

Sentinel	Sites	Functions
consensus.ErrPrunedAncestor	3	insertChain, insertSidechain, getResultBlock
consensus.ErrFutureBlock	2	insertChain
consensus.ErrUnknownAncestor	3	insertChain
ErrKnownBlock	3	insertChain, getResultBlock
ErrStopPreparingBlock	1	getResultBlock — err != ErrStopPreparingBlock → !errors.Is(err, ErrStopPreparingBlock) (negation preserved: only non-stop errors are reported as bad blocks)

Untouched by design: switch err { case ErrKnownBlock: ... } in prepareBlock (switch-case form, case nil branch present).

Testing

• gofmt / goimports clean, go vet ./core/ clean
• make all builds
• go test ./core/... — all pass
• make test — full suite, 0 FAIL
• make tidy / make generate — no changes

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[Copilot]

🟢 Approval recommended

The focused, mechanically consistent changes preserve current behavior while correctly supporting wrapped sentinel errors.

Pull request overview

Modernizes sentinel-error handling in blockchain insertion paths so wrapped errors are recognized correctly.

Changes:

• Replaces direct sentinel comparisons with errors.Is.
• Preserves negation when handling ErrStopPreparingBlock.

File summaries

File	Description
core/blockchain.go	Updates sentinel-error checks in block insertion and processing paths.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced

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