[3.x] 重构单测以支持 PgSql

[NHZEX]

暂定要解决的问题

1. pg insert 的自增主键获取需要重构为使用 returning 的方式才能更好解决 修改pgsql兼容，在事务内，没有自增id返回时，因为sql报错，事务中止，不能提交，只能回滚 #593
2. 需要提供一个 Model::maker 的重置方法，不然测试时全是重复的闭包
3. 当前没有做 pg 字段转义，需要添加双引号用于避免关键字冲突

[codecov]

Codecov Report

Attention: Patch coverage is 97.29730% with 1 line in your changes missing coverage. Please review.

Project coverage is 24.91%. Comparing base (52668c1) to head (e914992).
Report is 22 commits behind head on 3.0.

Files with missing lines	Patch %	Lines
src/db/connector/Pgsql.php	97.29%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.0     #773      +/-   ##
============================================
+ Coverage     22.61%   24.91%   +2.30%     
- Complexity     3113     3130      +17     
============================================
  Files            65       65              
  Lines          7465     7502      +37     
============================================
+ Hits           1688     1869     +181     
+ Misses         5777     5633     -144     

Flag	Coverage Δ
unittests	24.91% <97.29%> (+2.30%)	⬆️

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