feat: Adds RegionScanner trait

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

• Support parallel scan in mito engine #2806
• Partitioned scan for RegionEngine #3886

What's changed and what's your intention?

This PR adds the RegionScanner trait mentioned in #3886

pub trait RegionScanner: Debug + DisplayAs + Send + Sync {
    fn properties(&self) -> &ScannerProperties;
    fn schema(&self) -> SchemaRef;
    fn scan_partition(&self, partition: usize) -> Result<SendableRecordBatchStream, BoxedError>;
}

It allows us to split rows to scan into multiple partitions and increase scan parallelism. The RegionEngine has a new method handle_partitioned_query() to get the RegionScanner. It removes the old handle_query() method from the trait and only exposes it in the MitoEngine.

Since most region engines don't support partitioning, this PR adds a SinglePartitionScanner to turn a stream into a region scanner.

The execution plan returned by the dummy table provider now becomes the ReadFromRegion plan. This plan adapts a RegionScanner to the ExecutionPlan trait.

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.

[codecov]

Codecov Report

Attention: Patch coverage is 94.87179% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 85.18%. Comparing base (11ad5b3) to head (e400c17).
Report is 9 commits behind head on main.

Additional details and impacted files

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##             main    #3948      +/-   ##
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- Coverage   85.40%   85.18%   -0.22%     
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  Files         978      977       -1     
  Lines      169100   169323     +223     
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- Hits       144427   144245     -182     
- Misses      24673    25078     +405     

[v0y4g3r]

LGTM