fix(runtime): finish actor stateful integration semantics

[graydeon]

Summary

The actor runtime still has important stateful semantics covered only by ignored integration tests.

The ignored scenarios include:

• state updates across multiple messages
• multiple actor instances progressing independently
• actor state initialized with String values
• actor state mutation and retrieval workflows

Why this matters

• actors are a headline language/runtime capability
• the currently passing actor tests cover only a subset of the intended semantics
• ignored stateful cases make it hard to know which actor guarantees are reliable

Current behavior

Basic actor flows work, but several stateful integration scenarios remain ignored because the runtime/compiler path does not fully support them yet.

Expected behavior

Stateful actor workflows should be supported end-to-end, and the ignored actor integration tests should be runnable without ignore markers.

Suggested scope

• implement the missing actor state update/state mutation behavior
• fix String-carrying actor state paths if they require separate runtime handling
• unignore the affected actor integration tests
• add focused regression tests for repeated sends, asks, and independent actor state

Acceptance criteria

• ignored actor integration tests for state updates and actor state initialization are enabled
• actor state changes are observable through existing message/ask workflows
• multiple actor instances maintain independent state correctly