🧹 Refactor complex type ignoring map into list comprehension

[google-labs-jules]

🎯 What: Refactored complex nested map/lambda/join chains used to parse hexadecimal inputs into list comprehensions.
💡 Why: This improves the readability and maintainability of the BitVector module, making the code much more pythonic, and naturally resolves a type collision where list(hexlist) was being passed to map(chr, ...) triggering type ignores.
✅ Verification: Verified by ensuring the structural logic translated accurately via pytest run of the test suite (387 passing tests).
✨ Result: Cleaned up four unreadable map constructs into concise ~1-line list comprehensions under 20 lines each.

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PR created automatically by Jules for task 1153226975741967983 started by @schwehr

[google-labs-jules]

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