fix: stuck after restart when min filtered block is previous block of a check point

[yangby-cryptape]

Changes

• In the following code:

  https://github.com/nervosnetwork/ckb-light-client/blob/38aa9b200be7c6b96ded79bf3d2f84b157f2d230/src/protocols/light_client/peers.rs#L1606-L1608

  min_filtered_block_number is the last filtered block which has been synchronized.

  should_cached_check_point_index is the index of the check point, which contains the next filtered block which will be synchronized.

  So, the it should be fixed with following patch:

  pub(crate) fn update_min_filtered_block_number(&self, min_filtered_block_number: BlockNumber) { 
      let should_cached_check_point_index = 
  -         self.calc_best_check_point_index_not_greater_than(min_filtered_block_number); 
  +         self.calc_best_check_point_index_not_greater_than(min_filtered_block_number + 1); 

• See the following code:

  https://github.com/nervosnetwork/ckb-light-client/blob/38aa9b200be7c6b96ded79bf3d2f84b157f2d230/src/protocols/light_client/peers.rs#L1141-L1143

  At start, the check point index and the block number of it is 0, 0.

  The following check point index and the block number of it are 1, 2000, 2, 4000 and son on.

  When the client want to synchronizes the block 2000，the last check point should be 0.

  When the client want to synchronizes the block 2001 to 4000，the last check point should be 1.

  So, when client synchronizes the filtered block number, the check point should be:

  -         (number / self.check_point_interval) as u32 
  +         (number.saturating_sub(1) / self.check_point_interval) as u32

• Changed some naming to make the names are more appropriate.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (38aa9b2) 71.05% compared to head (e7499f3) 71.09%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #162 +/- ## =========================================== + Coverage 71.05% 71.09% +0.03% =========================================== Files 25 25 Lines 6420 6428 +8 =========================================== + Hits 4562 4570 +8 Misses 1858 1858 ``` | [Flag](https://app.codecov.io/gh/nervosnetwork/ckb-light-client/pull/162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/nervosnetwork/ckb-light-client/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork) | `71.09% <100.00%> (+0.03%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork#carryforward-flags-in-the-pull-request-comment) to find out more.

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