Fix client error handling

[abrookins]

We can't re-raise the original error because upstream, we expect a custom error, not the original.

[Copilot]

Pull Request Overview

This PR fixes client error handling by removing redundant raise statements after _handle_http_error calls. The _handle_http_error method already raises appropriate exceptions, so the additional raise statements were causing the original HTTPStatusError to be re-raised instead of the proper custom exceptions, breaking error handling flow.

• Removes redundant raise statements from all HTTP error handling blocks in the client
• Adds comprehensive test coverage for the get_or_create_working_memory method's 404 handling
• Updates version from 0.12.2 to 0.12.3

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
agent-memory-client/agent_memory_client/client.py	Removes redundant raise statements from HTTP error handling blocks across all API methods
agent-memory-client/tests/test_client.py	Adds test to verify proper 404 error handling in get_or_create_working_memory method
agent-memory-client/agent_memory_client/init.py	Updates package version to 0.12.3

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