feat: add uid attribute

[kiaking]

Add UID attribute.

Type of PR:

• Bugfix
• Feature
• Refactor
• Code style update
• Build-related changes
• Test
• Documentation
• Other, please describe:

Details

I had to modify few parts.

Model constructor

Previously, we were simply instantiating model when registering it to the database, or using in repository. Instead, now model accepts null as the constructor argument. When null is passed, all field value generation will be skipped.

Usually, users should never pass null. But pre-registered models don't require fields. It's better for performance, but also it avoids calling uuid multiple times making it hard to mock inside the test. Maybe we could add helper static function to model to create a new model instance without field, because we might for get to pass null in the future when creating new attributes.

Test

This is not new to this PR, but seems like we have to clear the model field registries on each test if we want to declare the same class in multiple test cases. For this, we can use Model.clearRegistries(). Note that we should not use this method for the test where we define class once and use same model in multiple tests. It is only for tests that define multiple same models.

[codecov]

Codecov Report

Merging #16 into master will decrease coverage by 0.24%.
The diff coverage is 98.11%.

@@            Coverage Diff             @@
##           master      #16      +/-   ##
==========================================
- Coverage   96.68%   96.44%   -0.25%     
==========================================
  Files          32       34       +2     
  Lines         754      787      +33     
  Branches      107      113       +6     
==========================================
+ Hits          729      759      +30     
- Misses         24       27       +3     
  Partials        1        1              

Impacted Files	Coverage Δ
src/model/Model.ts	89.68% <95.23%> (-0.15%)	⬇️
src/index.ts	100.00% <100.00%> (ø)
src/model/attributes/types/Uid.ts	100.00% <100.00%> (ø)
src/model/decorators/attributes/types/Uid.ts	100.00% <100.00%> (ø)
src/plugin/Plugin.ts	100.00% <100.00%> (ø)
src/query/Query.ts	94.70% <100.00%> (ø)
src/repository/Repository.ts	100.00% <100.00%> (ø)
src/schema/Schema.ts	97.56% <100.00%> (+1.26%)	⬆️
src/model/attributes/relations/HasOne.ts	94.11% <0.00%> (-5.89%)	⬇️
src/model/attributes/relations/HasMany.ts	94.11% <0.00%> (-5.89%)	⬇️
... and 4 more

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