This is a proposal to fix issue #507
**changes**
- `LambdaRuntime.init()` uses a `Mutex<Bool>` to make sure only one
instance is created
- `LambdaRuntime.init()` can now throw an error in case an instance
already exists (I did not use `fatalError()` to make it easier to test)
- All `convenience init()` methods catch possible errors instead of
re-throwing it to a void breaking the user-facing API
- Renamed existing `LambdaRuntimeError` to `LambdaRuntimeClientError`
- Introduced a new type `LambdaRuntimeError` to represent the double
initialization error
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Co-authored-by: Fabian Fett <fabianfett@apple.com>
Co-authored-by: Adam Fowler <adamfowler71@gmail.com>
Sébastien Stormacq
Fabian Fett