Refactor/improve THP device tests

[M1nd3r]

• Blocked by: PR #6273 - trezorlib 0.20 release refactor - the trezorlib refactor needs to be merged first to avoid unnecessary merge conflicts.

Tests in test/device_tests/thp/ are in need of refactoring and improvements. It would be nice to improve the test infrastructure/setup - to have a way to create a DebugClient or DebugSession in specific pairing state, with specific pairing path (CodeEntry/Nfc/Qr Code), or to be able to create/get valid pairing credentials more easily.

Additionally, add tests for more "code branches" - e.g. branches that result in DataError during pairing. See #6284 for branches overview and test examples.

Note: this can be fixed, too: #6284 (comment)