Fix tidy-viewer-py build error

[alexhallam]

Make tidy-viewer-py installable from source distribution by vendoring tidy-viewer-core and making dependencies self-contained.

When pip install attempts to build tidy-viewer-py from a source distribution, it lacks access to the parent workspace's tidy-viewer-core crate and workspace-level dependency definitions. This PR resolves the build failure by including tidy-viewer-core directly within the package, updating Cargo.toml files to use explicit dependency versions, and adding a MANIFEST.in to ensure all necessary Rust source files are included in the source distribution.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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