Adds `_internal_test.go` files to test unexported functions in the `crypt` and `lthn` packages, improving overall test coverage.
- Adds tests for the `ensureRSA` private function in `pkg/crypt/crypt.go`.
- Adds tests for the `createSalt` private function in `pkg/crypt/std/lthn/lthn.go`.
These changes align with the project's TDD methodology and follow the `_Good`, `_Bad`, `_Ugly` testing structure.
