[SDK-2752] Expand test coverage and finish migration to Pest framework

[evansims]

Changes

Although this PR is large and intimidating to look it, it doesn't change anything regarding the logic of the SDK. Its purpose is to expand the unit tests to 100% coverage of the v8 SDK, and to update our unit test syntax to the modern Pest format we had already adopted with our newer test additions in v8.

The highlighted intent of this pull request:

• Expands the test coverage of our unit tests for 8.0 to 100%
• Rebuilds our legacy PHPUnit tests using the modern Pest test framework syntax
• Adopts expectations and higher order tests
• Adds the pest-plugin-parallel plugin for improved performance by running tests in parallel
• Adds hyperf/event to dev dependencies for thorough PSR-4 unit testing

Other tweaks in this PR of note:

• Renamed the newly contributed InMemoryStorage class to MemoryStore to match the naming convention of other storage classes. As it is new to v8, this is not a breaking change.
• References to the internal httpClient var in the ManagementEndpoint class now use the public getHttpClient() method to ensure the HTTP client is properly instantiated before its use.
• Renamed the methods on Auth0\SDK\API\Management\Tenants to match the naming conventions of other Management classes, which follow the naming conventions of the endpoints themselves.
• Fixed a bug with handleInvitation() on the Auth0\SDK\Auth0 in which the login URL was not properly returned.
• Added an argument to clear() on Auth0\SDK\Auth0 to opt out of clearing transient storage, in the event we're only needing to wipe out a stale user session to make way for a new one during code exchange.
• Added an argument to getRequestParameter() on Auth0\SDK\Auth0 to support applying different internal PHP sanitization filters.
• Removed some unnecessary code from SdkConfiguration which is now handled by improved type checking in ConfigurableMixin.
• Added support for mocked HTTP responses to TokenVerifier for unit testing purposes.
• Added code coverage metablocks in fringe portions of the SDK that cannot be tested (for example in the event a PHP runtime was built to not return it's version, or isn't compiled with OpenSSL, etc.)
• Made some bug fixes to the Toolkit in regard to object referencing.

Testing

Tests can be run locally using composer run tests, or in a Docker container using composer run tests:docker.

Contributor Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct

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