[Enhancement] Add retry logic with exponential backoff

[talltechy]

Description

Add automatic retry with exponential backoff for transient API failures to improve reliability.

Features

• Automatic retry on transient failures (500, 502, 503, 504)
• Exponential backoff strategy
• Configurable max retry attempts
• Configurable backoff multiplier
• Rate limit (429) handling with Retry-After header respect
• Timeout handling

Acceptance Criteria

• Retry decorator or mixin implemented
• Applied to BaseAPI._request() method
• Configurable via environment variables
• Proper logging of retry attempts
• Rate limit handling with Retry-After
• Unit tests for retry logic
• Documentation updated

Technical Approach

# Example configuration
INSIGHTVM_MAX_RETRIES=3
INSIGHTVM_BACKOFF_FACTOR=2
INSIGHTVM_RETRY_STATUSES=500,502,503,504

Context

Part of Sprint 4: Error Handling (4-6 hours)

Currently no automatic retry for transient failures. This will improve resilience in production.

See: memory-bank/github-workflow.md for workflow details