Simpler error strategy

[slinkydeveloper]

Fix #101

This implements a (IMO) simpler error strategy, less error prone:

• Every thrown failure that is a StatusRuntimeException or a StatusException, or every failure passed to StreamObserver#onError is a terminal failure
• In all the other cases is a non terminal failure

It adds a bit of "asymmetry" wrt the error types, due to StreamObserver#onError, but i believe this is fine, because the user intentionally calls StreamObserver#onError (as opposed to runtime exceptions that might just be thrown by 3rd party libraries)

[github-actions]

Unit Test Results

144 tests  ±0   144 ✔️ ±0   9s ⏱️ -1s
  14 suites ±0       0 💤 ±0 
  14 files   ±0       0 ❌ ±0 

Results for commit 7e25551. ± Comparison against base commit e1a6389.

This pull request removes 10 and adds 10 tests. Note that renamed tests count towards both.

dev.restate.sdk.core.impl.UserFailuresTest ‑ 10: [UNBUFFERED_MULTI_THREAD] ThrowStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 11: [BUFFERED_SINGLE_THREAD] ResponseObserverOnErrorStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 12: [UNBUFFERED_MULTI_THREAD] ResponseObserverOnErrorStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 3: [BUFFERED_SINGLE_THREAD] ThrowUnknownStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 4: [UNBUFFERED_MULTI_THREAD] ThrowUnknownStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 5: [BUFFERED_SINGLE_THREAD] ResponseObserverOnErrorIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 6: [UNBUFFERED_MULTI_THREAD] ResponseObserverOnErrorIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 7: [BUFFERED_SINGLE_THREAD] SideEffectThrowIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 8: [UNBUFFERED_MULTI_THREAD] SideEffectThrowIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 9: [BUFFERED_SINGLE_THREAD] ThrowStatusRuntimeException

dev.restate.sdk.core.impl.UserFailuresTest ‑ 10: [UNBUFFERED_MULTI_THREAD] ResponseObserverOnErrorStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 11: [BUFFERED_SINGLE_THREAD] ResponseObserverOnErrorIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 12: [UNBUFFERED_MULTI_THREAD] ResponseObserverOnErrorIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 3: [BUFFERED_SINGLE_THREAD] SideEffectThrowIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 4: [UNBUFFERED_MULTI_THREAD] SideEffectThrowIllegalStateException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 5: [BUFFERED_SINGLE_THREAD] ThrowStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 6: [UNBUFFERED_MULTI_THREAD] ThrowStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 7: [BUFFERED_SINGLE_THREAD] ThrowUnknownStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 8: [UNBUFFERED_MULTI_THREAD] ThrowUnknownStatusRuntimeException
dev.restate.sdk.core.impl.UserFailuresTest ‑ 9: [BUFFERED_SINGLE_THREAD] ResponseObserverOnErrorStatusRuntimeException

[tillrohrmann]

I think the model is simpler now with every StatusException, StatusRuntimeException and responseObserver.onError() call being a terminal exception.