Add PartiqlSharedCatalog for Send+Sync catalog usage.

[jpschorr]

• Splits the Catalog interface into a MutableCatalog and a ReadOnlyCatalog.
• Adds SharedCatalog: ReadOnlyCatalog + Send + Sync
• Adds PartiqlSharedCatalog which impls SharedCatalog

TODO:

• Add tests for shared usage

Addresses #579

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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.

[github-actions]

Conformance comparison report

	Base (2ae6c4e)	ca9a88c	+/-
% Passing	87.89%	87.89%	0.00%
✅ Passing	5863	5863	0
❌ Failing	808	808	0
🔶 Ignored	0	0	0
Total Tests	6671	6671	0

Number passing in both: 5863

Number failing in both: 808

Number passing in Base (2ae6c4e) but now fail: 0

Number failing in Base (2ae6c4e) but now pass: 0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.13%. Comparing base (2ae6c4e) to head (ed3a181).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #583   +/-   ##
=======================================
  Coverage   81.13%   81.13%           
=======================================
  Files         110      110           
  Lines       21792    21796    +4     
  Branches    21792    21796    +4     
=======================================
+ Hits        17681    17685    +4     
  Misses       3593     3593           
  Partials      518      518           

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