[amol-]

The lazy session proxy does not delegate len(), so callers receive TypeError. Delegate length to the underlying session, including its reserved metadata keys, without changing other proxy behavior.

Validation:

• Regression covers lazy initialization and length changes after insertions and deletion.
• All 7 existing/new TestSessionObject tests passed from a temporary working directory.
• git diff --check passed; code-quality review approved the unchanged diff.

Fixes #30