Implement comprehensive versioning strategy with branch-based version management

[Copilot]

This PR implements a comprehensive versioning strategy for the rate-envelope-queue project based on the requirements in issue #14. The strategy uses branch-based version management to support multiple versions simultaneously with clear lifecycle management.

Key Features

📋 Branch Structure

• Version branches: v1, v2, v3, etc. for stable releases
• Pre-release branches: pre-release-v1, pre-release-v2, etc. for testing and integration
• Main branch: Always points to the current maximum major version for repository readability

🔄 Version Lifecycle Management

• Active support: New features and bug fixes
• Stabilization mode: Only bug fixes (when version +1 exists)
• Deprecated status: Critical security fixes only (when stable version +2 exists)
• End-of-life: No support (when stable version +3 exists)

🛠 Development Workflow

The strategy implements a clear development flow:

feature branches → pre-release-vX → vX → release tags

Developers create feature branches from pre-release branches, test and integrate in pre-release, then merge to stable version branches for tagging.

Implementation Details

Documentation

• VERSIONING.md: Complete strategy guide in Russian with examples
• CONTRIBUTING.md: Developer workflow guide with practical examples
• POST_MERGE_SETUP.md: Step-by-step setup instructions for maintainers
• Updated README.md with version support matrix and installation examples

Automation Tools

• setup-versioning.sh: Automated script for creating version branch structure
• GitHub Actions workflows: CI/CD for version branches and automated releases
• Enhanced .gitignore: Excludes build artifacts and temporary files

Example Usage

# Create version structure
./setup-versioning.sh v1

# Development workflow
git checkout pre-release-v1
git checkout -b feature/new-feature
# ... develop and test ...
# PR to pre-release-v1 → test → merge to v1 → create release tag

The strategy supports concurrent development across multiple versions while maintaining clear separation and lifecycle management. All changes maintain backward compatibility and the existing codebase builds and tests successfully.

Fixes #14.

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