feat: add deterministic Rust snapshot generator

[tomatotomata]

Summary

• add a focused snapshot_generator workspace member for deterministic Rust Bloom and Count-Min snapshots
• expose it through cargo x generate-snapshots
• document the local generated-output workflow and keep generated .sk files ignored

Validation

• cargo +stable check --workspace
• cargo +stable run -p x -- generate-snapshots
• cargo +stable fmt --all
• git diff --check

The implementation was prepared with AI assistance and reviewed by me. I am responsible for the changes and this submission.

Closes #176