Restore Taiko FCU timestamp validation allowing equal timestamps

[Copilot]

Taiko Pacaya allows multiple L2 blocks derived from a single L1 block, all sharing the same L1 anchor timestamp — so equal timestamps must be accepted. This was broken in #10325, which renamed ArePayloadAttributesTimestampAndSlotNumberValid, dropped virtual, and deleted the Taiko override.

Changes

• Add protected virtual ulong GetMinRequiredTimestamp(Block newHeadBlock) => newHeadBlock.Timestamp + 1; to ForkchoiceUpdatedHandler, used by the timestamp validation logic
• ArePayloadAttributesTimestampAndSlotNumberValid is now non-virtual (delegates threshold to GetMinRequiredTimestamp)
• TaikoForkchoiceUpdatedHandler overrides only the one-liner: => newHeadBlock.Timestamp (allowing >= instead of >)

// ForkchoiceUpdatedHandler
protected virtual ulong GetMinRequiredTimestamp(Block newHeadBlock) => newHeadBlock.Timestamp + 1;

// TaikoForkchoiceUpdatedHandler
protected override ulong GetMinRequiredTimestamp(Block newHeadBlock) => newHeadBlock.Timestamp;

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

Testing

Requires testing

• Yes
• No

If yes, did you write tests?

• Yes
• No

Notes on testing

Added 3 test cases in TaikoEngineApiTests: equal timestamp accepted, greater timestamp accepted, lesser timestamp rejected.

Documentation

Requires documentation update

• Yes
• No

Requires explanation in Release Notes

• Yes
• No

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