Refactor: package-wide lazy-loading utility

[cagataycali]

Context

PR #56 review — @awsarron noted lazy import patterns are scattered across the package. Suggested a package-wide reusable lazy imports loader.

Problem

Multiple __init__.py files implement ad-hoc __getattr__ for lazy loading. require_optional() in utils.py handles import-or-fail but not deferred loading.

Proposed Solution

Create a reusable lazy-loading utility in strands_robots/utils.py that all __init__.py files can use, reducing boilerplate and ensuring consistency.

Acceptance Criteria

• Single utility for lazy imports
• All __getattr__ lazy imports migrated
• Tests verify lazy behavior

Ref: PR #56 review threads