Refactor equality as per spec. eqg and add testing equality ops

[jpschorr]

This change refactors equality to more closely (and more visibly) reflect the specification's description in 7.1.1

This change also adds the ability to perform comparisons where NULL == NULL and/or NaN == NaN for the purposes of asserting test results more easily.

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

[codecov]

Codecov Report

Attention: Patch coverage is 80.61224% with 19 lines in your changes missing coverage. Please review.

Project coverage is 81.18%. Comparing base (3647c56) to head (375abaa).

Files with missing lines	Patch %	Lines
partiql-value/src/comparison.rs	77.77%	6 Missing ⚠️
partiql-value/src/value.rs	63.63%	4 Missing ⚠️
partiql-value/src/bag.rs	85.00%	3 Missing ⚠️
partiql-value/src/list.rs	78.57%	3 Missing ⚠️
partiql-value/src/tuple.rs	81.25%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #537      +/-   ##
==========================================
- Coverage   81.27%   81.18%   -0.10%     
==========================================
  Files          90       90              
  Lines       19672    19730      +58     
  Branches    19672    19730      +58     
==========================================
+ Hits        15988    16017      +29     
- Misses       3264     3293      +29     
  Partials      420      420              

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[github-actions]

Conformance comparison report

	Base (3647c56)	db26def	+/-
% Passing	86.90%	86.97%	0.06%
✅ Passing	5587	5591	4
❌ Failing	842	838	-4
🔶 Ignored	0	0	0
Total Tests	6429	6429	0

Number passing in both: 5587

Number failing in both: 838

Number passing in Base (3647c56) but now fail: 0

Number failing in Base (3647c56) but now pass: 4

The following test(s) were previously failing but now pass. Before merging, confirm they are intended to pass:

Click here to see

• partiql_tests::eval::ion::query::query::group_by::group_by::simple_group_by::strict_group_by_with_where
• partiql_tests::eval::ion::query::query::group_by::group_by::simple_group_by::strict_group_by_with_group_as_and_where
• partiql_tests::eval::ion::query::query::group_by::group_by::simple_group_by::permissive_group_by_with_where
• partiql_tests::eval::ion::query::query::group_by::group_by::simple_group_by::permissive_group_by_with_group_as_and_where