Feature request: ORMPurger cache statements

[dmitryuk]

I use ORMPurger on every test in setUp method:

1. Call $this->getFixtureExecutor()->execute($this->getFixtureLoader()->getFixtures());.
2. ORMExecutor internally calls $this->purger->purge(); independently of fixtures passed
3. ORMPurger::purge do a lot of manipulations (use metadata, getSchemaAssetsFilter, getFilterSchemaAssetsExpression, etc), and finally run sql statements.

I think it is possible to prevent extra manipulations in ORMPurger and cache, reuse sql statements. What do you think? What type of cache we can use (static variable, for example)?

[dmitryuk]

Benchmark results on 704 tests.

• Before Time: 05:17.942, Memory: 323.00 MB
• With caching sql statements of ORMPurger Time: 04:36.265, Memory: 277.00 MB

[dmitryuk]

Completed, thanks