Improvements to pretty-printing for AND/OR/CASE

[jpschorr]

Addresses parts of #473 :

• Improves pretty-printing of CASE
• adds round-trip testing for pretty-printing

Also:

• Improves pretty-printing of AND/OR connectives
• Improves pretty-printing of query clauses

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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 98.90110% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.00%. Comparing base (2da9cdb) to head (6b546aa).

Files	Patch %	Lines
partiql-ast/src/pretty.rs	98.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #482      +/-   ##
==========================================
+ Coverage   80.98%   81.00%   +0.02%     
==========================================
  Files          68       68              
  Lines       18680    18704      +24     
  Branches    18680    18704      +24     
==========================================
+ Hits        15128    15152      +24     
- Misses       3109     3110       +1     
+ Partials      443      442       -1     

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[github-actions]

Conformance comparison report

	Base (2da9cdb)	933ef51	+/-
% 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 (2da9cdb) but now fail: 0

Number failing in Base (2da9cdb) but now pass: 0

[am357]

LGTM—with one suggestion to remove the lines that are commented out.