Implement MmapBitVector backend

[google-labs-jules]

This commit adds BitVector/mmap_bitvector.py which contains MmapBitVector. This new class implements BitVectorProtocol using a file-backed mmap mapping via Python's tempfile module.

Performance Comparison:
Using 10,000 bits mapped into memory per instance, we compare XOR performance:

• Standard BitVector: ~0.119 s / 1000 iter
• MmapBitVector: ~0.428 s / 1000 iter

The overhead is largely from Python's byte-level looping inside magic methods (doing bitwise operation character/byte wise for arbitrary lengths in memory versus BitVector's block optimized structure on an array.array). Although int.from_bytes translations make initialization and int_val reads very fast, operations requiring iteration over the underlying buffer take longer due to looping via standard Python indexing without native chunk optimizations.

---

PR created automatically by Jules for task 7990074438894762523 started by @schwehr

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.