feat: provide detailed polars column metadata

[brianheineman]

Addresses #240

For the given JSON:

{
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [
      -104.820246,
      41.139981
    ]
  },
  "properties": {
    "name": "Center of Cheyenne, Wyoming"
  }
}

Prior to these changes, the column metadata was:

        Column        |   Type    | Not null | Default 
----------------------+-----------+----------+---------
 type                 | str       | Yes      |         
 geometry             | struct[2] | Yes      |         
 properties           | struct[1] | Yes      |         

With these changes, the column metadata is now:

        Column        |   Type    | Not null | Default 
----------------------+-----------+----------+---------
 type                 | str       | Yes      |         
 geometry             | struct[2] | Yes      |         
 geometry.type        | str       | Yes      |         
 geometry.coordinates | list[f64] | Yes      |         
 properties           | struct[1] | Yes      |         
 properties.name      | str       | Yes      |        

The coordinates can be retrieved with the following SQL:

SELECT
    geometry.coordinates[1] AS longitude,
    geometry.coordinates[2] AS latitude
FROM
    cheyenne

[github-actions]

Bencher Report

Branch	improve-polars-metadata
Testbed	localhost

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Benchmark	Latency	nanoseconds (ns)
postgres-embedded	📈 view plot ⚠️ NO THRESHOLD	829,180,000.00
postgresql-embedded	📈 view plot ⚠️ NO THRESHOLD	839,600,000.00
rusqlite	📈 view plot ⚠️ NO THRESHOLD	4,465,400.00
sqlite	📈 view plot ⚠️ NO THRESHOLD	4,774,800.00

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[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 93.62%. Comparing base (88742b8) to head (2077d65).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
rsql_drivers/src/polars/metadata.rs	86.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #245      +/-   ##
==========================================
- Coverage   93.64%   93.62%   -0.03%     
==========================================
  Files         108      108              
  Lines       13433    13453      +20     
==========================================
+ Hits        12580    12596      +16     
- Misses        853      857       +4     

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