fix(runtime): keep state versions consistent and emit versioned state deltas

[Kushagra7777]

Why

State and version were read separately during serialization, allowing an older state to be labelled with a newer version.

The runtime also sent full snapshots for every update, even when only a small field changed.

Changes

• Publish state and version together as an atomic snapshot.
• Use that snapshot for streamed updates and GetCurrentState responses.
• Generate JSON Merge Patches when both the patch payload and complete protobuf message are smaller than a full update.
• Track the last emitted state and version separately for each subscription.
• Start every subscription with a full snapshot.
• Handle skipped versions without assuming consecutive version numbers.
• Fall back to full snapshots for unsupported input, excessive nesting, unrepresentable explicit-null changes, or patches without size savings.
• Keep GetCurrentState responses as full snapshots.

Tests

Added regression coverage for:

• Updates occurring during snapshot and stream serialization.
• Concurrent state updates, immediate state reads, and equal-state updates.
• Initial full snapshots followed by deltas.
• Independent subscription baselines.
• Skipped versions and exact delta base versions.
• Nested edits, field deletion, and array replacement.
• Explicit-null fallback and subsequent delta recovery.
• Unsupported JSON, invalid UTF-8, excessive nesting, and patches without payload savings.

A local test run reported 276 tests with zero failures, errors, or skips.

Validation limits

The reported 276-test run preceded correcting two implementation files that were accidentally placed under src/test. Both files are now under src/main; a clean build and test result after that move still needs to be recorded.

The new service tests call the service directly. End-to-end host integration, transport reconnection, child-process restart behavior, and representative performance benchmarks remain unverified.

Dependency

This branch is based on the runtime IPC baseline from PR #21
(d98614e). That prerequisite work belongs to its original contributor.

Related to #20; this PR does not claim to complete the entire issue.