Bugfixes and `SchemaPrinter` improvements.

☣	Breaking changes

Features

• graphql/SchemaPrinter: SchemaPrinter contract extended with two new methods SchemaPrinter::getLevel() and SchemaPrinter::setLevel(). (98953bf) ☣
• graphql/SchemaPrinter: Implemented SchemaTypePrinter (to print Type and all its used types/directives) and assertGraphQLSchemaTypeEquals() assertion. (cc581cf)
• graphql/SchemaPrinter: Implemented TypePrinter (to print one single Type) and assertGraphQLTypeEquals() assertion. (1828e8c)

Bug Fixes

• graphql/SchemaPrinter: Directives indent in description. (33c4505), closes #16
• testing: CronableAssertions::assertCronableRegistered(): "TypeError: str_contains(Argument #1 ($haystack) must be of type string, null given". (cc878d2)

Code Refactoring

• graphql/SchemaPrinter: Printer contract renamed to SchemaPrinter. (2ddad1b) ☣

Security

• Minimal version of guzzlehttp/psr7 v1.x set to 1.8.5 (CVE-2022-24775) (f6b5ef3) ☣
• Minimal version of guzzlehttp/psr7 v2.x set to 2.1.1 (CVE-2022-24775) (82995e7) ☣