Add metas to PartiQL Common

[am357]

Description of changes:

Adds an implementation for storing metadata for PartiQL objects. Currently, the implementation does not include any traits. It introduces PartiqlMetadata and PartiqlMetaValue structures:

        let foo_val = PartiqlMetaValue::String("foo".to_string());
        let i64_val = PartiqlMetaValue::Int64(2);

        let expected_vec_val = vec![foo_val, i64_val];
        let expected_bool_val = true;
        let expected_int_val = 2;
        let expected_float_val = 2.5;
        let expected_str_val = "foo";

        let mut expected_map = PartiqlMetadata::new();
        expected_map.insert("bool value", expected_bool_val.into());
        expected_map.insert("integer value", expected_int_val.into());

        let mut metas = PartiqlMetadata::new();
        metas.insert("vec value", expected_vec_val.clone().into());
        metas.insert("bool value", expected_bool_val.into());
        metas.insert("integer value", expected_int_val.into());
        metas.insert("float value", expected_float_val.into());
        metas.insert("string value", expected_str_val.into());
        metas.insert("map value", expected_map.clone().into());

        let vec_val = metas.vec_value("vec value").expect("vec meta value");
        let bool_val = metas.bool_value("bool value").expect("bool meta value");
        let int_val = metas.i32_value("integer value").expect("i32 meta value");
        let float_val = metas.f64_value("float value").expect("f64 meta value");
        let string_val = metas.string_value("string value").expect("string meta value");
        let map_val = metas.map_value("map value").expect("map meta value");

        assert_eq!(vec_val, expected_vec_val.clone());
        assert_eq!(bool_val, expected_bool_val.clone());
        assert_eq!(int_val, expected_int_val.clone());
        assert_eq!(float_val, expected_float_val.clone());
        assert_eq!(string_val, expected_str_val);
        assert_eq!(map_val, expected_map.clone());

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

Conformance comparison report

	Base (7203852)	1273b62	+/-
% Passing	90.35%	90.35%	0.00%
✅ Passing	5731	5731	0
❌ Failing	612	612	0
🔶 Ignored	0	0	0
Total Tests	6343	6343	0

Number passing in both: 5731

Number failing in both: 612

Number passing in Base (7203852) but now fail: 0

Number failing in Base (7203852) but now pass: 0

[codecov]

Codecov Report

Attention: Patch coverage is 46.76617% with 107 lines in your changes missing coverage. Please review.

Project coverage is 80.61%. Comparing base (7203852) to head (42816dd).
Report is 1 commits behind head on main.

Files	Patch %	Lines
partiql-common/src/metadata.rs	46.76%	107 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #488      +/-   ##
==========================================
- Coverage   80.98%   80.61%   -0.37%     
==========================================
  Files          69       70       +1     
  Lines       18796    18997     +201     
  Branches    18796    18997     +201     
==========================================
+ Hits        15221    15315      +94     
- Misses       3131     3238     +107     
  Partials      444      444              

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