Verify that there can't be two handlers with same name

[slinkydeveloper]

Fix #322

[github-actions]

Test Results

 48 files  ±0   48 suites  ±0   3m 5s ⏱️ -2s
738 tests ±0  730 ✅ +1  8 💤  - 1  0 ❌ ±0 
738 runs   - 1  730 ✅ ±0  8 💤  - 1  0 ❌ ±0 

Results for commit 824a5cf. ± Comparison against base commit 2b5d8e4.

This pull request removes 7 and adds 7 tests. Note that renamed tests count towards both.

dev.restate.e2e.NodeWorkflowAPITest ‑ Workflow cannot be submitted more than once
dev.restate.sdk.common.CoreSerdesTest ‑ Byte: -111
dev.restate.sdk.common.CoreSerdesTest ‑ Double: 0.5184783207844548
dev.restate.sdk.common.CoreSerdesTest ‑ Float: 0.62707436
dev.restate.sdk.common.CoreSerdesTest ‑ Integer: 1461953937
dev.restate.sdk.common.CoreSerdesTest ‑ Long: -4178086973975213529
dev.restate.sdk.common.CoreSerdesTest ‑ Short: 13800

dev.restate.sdk.common.CoreSerdesTest ‑ Byte: -45
dev.restate.sdk.common.CoreSerdesTest ‑ Double: 0.8948854648588914
dev.restate.sdk.common.CoreSerdesTest ‑ Float: 0.8062008
dev.restate.sdk.common.CoreSerdesTest ‑ Integer: 1743726599
dev.restate.sdk.common.CoreSerdesTest ‑ Long: -8028845254367141477
dev.restate.sdk.common.CoreSerdesTest ‑ Short: 19725
dev.restate.sdk.serde.jackson.JacksonSerdesTest ‑ [Till, Francesco]

♻️ This comment has been updated with latest results.