Improved typing of PermissionGrant.parse() to avoid misuse

[thehenrytsai]

1. Improved typing of PermissionGrant.parse() to avoid misuse
2. Detected and fixed a couple of unimportant misuses in the tests after the above change (case in point).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.64%. Comparing base (158470f) to head (2d5cf5f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #760 +/- ## ========================================== + Coverage 98.57% 98.64% +0.07% ========================================== Files 73 73 Lines 10986 10987 +1 Branches 1582 1585 +3 ========================================== + Hits 10829 10838 +9 + Misses 151 143 -8 Partials 6 6 ```

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