fix(light-client): could not check MMR for fork chains

[yangby-cryptape]

What problem does this PR solve?

Problem Summary:

The MMR data are saved as key-value format and the keys are positions (= block_number - MMR_enabled_block_number).

ckb/store/src/transaction.rs

Lines 371 to 376 in 922516e

	let position: packed::Uint64 = position_u64.pack();
	self.insert_raw(
	COLUMN_CHAIN_ROOT_MMR,
	position.as_slice(),
	header_digest.as_slice(),
	)

So, only the MMR data for main chain could be fetched from the storage.

ckb/util/light-client-protocol-server/src/components/get_last_state_proof.rs

Line 150 in 922516e

let mmr = self.snapshot.chain_root_mmr(*number - 1);

What is changed and how it works?

What's Changed:

• CKB node sends the hash of block H to light client.
• Then CKB node changes to a fork chain which tip is block G.
• Light client asks CKB node for proof of the chain whose tip is block H.
• Difference:
  • Before the bugfix:
    • CKB node sends a proof base on block H with a incorrect MMR proof to light client.
    • Light client checks the incorrect MMR proof, then ban CKB node for 300 seconds.
  • After this bugfix:
    • CKB node sends the hash of block G to light client.

Check List

Tests

• Unit test
• Integration test

Release note

Title Only: Include only the PR title in the release note.

[yangby-cryptape]

Waiting for #4172 merged.