type constraints validate ScalarValue and return valid Datum

[alex-dukhno]

Closes #310 #218

Description

type constraints validate ScalarValue and return valid Datum

Client output

No changes to client output

[coveralls]

Pull Request Test Coverage Report for Build 252721346

• 312 of 319 (97.81%) changed or added relevant lines in 8 files are covered.
• 17 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.4%) to 88.401%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/query_planner/src/planner/update.rs	4	5	80.0%
src/query_planner/src/planner/insert.rs	8	10	80.0%
src/constraints/src/lib.rs	267	271	98.52%

Files with Coverage Reduction	New Missed Lines	%
src/sql_engine/src/dml/insert.rs	1	65.67%
src/ast/src/lib.rs	16	46.96%

Totals
Change from base Build 252403339:	0.4%
Covered Lines:	7576
Relevant Lines:	8570

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💛 - Coveralls