[Feature] Implement a Client

[antstorm]

What was changed

Adding a Client implementation to communicate with the Temporal server

Why?

Crucial part of the SDK

Checklist

1. Closes #4

2. How was this tested: Integration tests with the Temporalite included, unit test to follow

3. Any docs updates needed? No

[antstorm]

Please note that there are a few features intentionally left out to keep the PR size contained (which was achieved with various degrees of success 😅). The follow ups include:

• Updating RBS signatures
• Add YARD comments with argument descriptions for public API
• Write unit tests for all newly added classes
• Abstract Proto serializers
• Implement serialization for RetryPolicy
• Implement converters and codecs
• Define exception hierarchy and use it instead of the blanket Temporal::Error
• Implement follow_runs for await_workflow_result
• Add timeouts to await_workflow_result