fix: full project modernization, tests, python 3.10 compatibility

[zbowling]

This commit modernizes warctools for Python 3.10+ with comprehensive improvements to code quality, testing, and tooling:

Project Structure:

• Migrate to src/ layout for proper package structure
• Move hanzo package to src/hanzo/
• Add src/warctools/ for backward compatibility re-exports
• Update build system to uv_build backend

Code Modernization:

• Remove all future imports (Python 3.10+ only)
• Add comprehensive type hints throughout codebase
• Migrate all CLI tools from optparse to click (100% argument compatible)
• Update f-string usage and modernize string formatting
• Remove unnecessary object inheritance (UP004)
• Fix all linting issues (ruff, mypy) systematically

Dependencies & Build:

• Increment version to 6.0.0
• Update requires-python to >=3.10
• Add click>=8.0.0 dependency
• Switch from setuptools to uv_build
• Add dev dependencies: pytest, ruff, mypy

Testing:

• Add comprehensive integration test suite (15 tests)
• Add CLI help tests for all tools
• Fix legacy unittest offset calculation bugs
• All 33 tests passing (integration + unit + CLI)

CI/CD:

• Add GitHub Actions workflow for automated testing
• Update Travis CI configuration for modern Python versions
• Run ruff format, ruff check, mypy, and pytest in CI

Bug Fixes:

• Fix gzip member offset tracking in GzipRecordStream
• Fix RecordStream offset calculation for accurate record positioning
• Fix exception handling and error messages
• Fix variable naming issues (B007, N806, E741)
• Fix import ordering and unused imports

Documentation:

• Add AGENTS.md for future AI agent guidance
• Document project layout, build process, and tool preferences

All tools tested and verified working on real-world WARC archives.

[zbowling]

I hit a few bugs and when I went to try and debug I noticed this project didn't use a lot of modern python things. I went nuts here. You don't have to accept this form like this because I know it's a lot but I added signficant tests, modernized the code, switch the arg parser, etc. Brought the code from 2012 era python to 2025 python.