Docs: add documentation about basic test patterns

[leandrodamascena]

Create documentation for basic test patterns in durable functions, showing developers how to write simple, effective tests with common assertion patterns.

Solution

Create basic test patterns docs with:

• Basic test structure - Simple test examples with the testing framework
• Status checking patterns - How to verify execution status (SUCCEEDED, FAILED, etc.)
• Result verification - Patterns for asserting on function results
• Operation assertions - How to verify individual operations (steps, waits, callbacks)
• Test organization - Tips for structuring test files and test cases
• Common patterns - Frequently used assertion patterns
• Simple examples - Clear, minimal examples that demonstrate each pattern
• Best practices - Guidelines for writing maintainable tests