weavegraph 0.3.0

Graph-driven, concurrent agent workflow framework with versioned state, deterministic barrier merges, and rich diagnostics.
Documentation
## Description

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## Related Issues

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Closes #

## Type of Change

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- [ ] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)
- [ ] Documentation update
- [ ] Refactoring (no functional changes)
- [ ] Performance improvement
- [ ] Test improvements

## Changes Made

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- 
- 
- 

## Testing

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- [ ] Existing tests pass (`cargo test`)
- [ ] Added new tests for changes
- [ ] Tested manually (describe how)

**Test environment:**
- Rust version: 
- OS: 

## Checklist

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- [ ] My code follows the project's code style (`cargo fmt`)
- [ ] I have run clippy and addressed warnings (`cargo clippy`)
- [ ] I have updated documentation (if needed)
- [ ] I have added tests that prove my fix/feature works
- [ ] All tests pass locally
- [ ] I have updated CHANGELOG.md (if user-facing change)
- [ ] I have checked that no breaking changes are introduced (or documented them)

## Breaking Changes

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N/A

## Additional Notes

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