fix(remote_wal): some known issues

[niebayes]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

• Rewrite the iteration in append_batch to ensure the region_ids and last_entry_ids coincide.
• Temporarily replace the DashMap with tokio::sync::Mutex to resolve a known deadlock issue.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

[WenyXu]

Rest LGTM

[codecov]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (7551432) 85.50% compared to head (b2a0802) 85.41%.
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3052      +/-   ##
==========================================
- Coverage   85.50%   85.41%   -0.10%     
==========================================
  Files         794      799       +5     
  Lines      128555   129037     +482     
==========================================
+ Hits       109924   110220     +296     
- Misses      18631    18817     +186     

[v0y4g3r]

LGTM

[WenyXu]

Adding a scope can avoid releasing the lock manually.

  {
          let client_pool = self.client_pool.read().await;
          if let Some(client) = client_pool.get(topic) {
              return Ok(client.clone());
          }
  }