fix: validate tao ss58 checksums

[volcano303]

Summary

• validate TAO addresses with Bittensor's SS58 checksum validator instead of regex-only shape checks
• add regression coverage for checksum-mutated and base58-shaped invalid addresses

Issue

Closes #200

Validation

• uv run ruff check allways/ neurons/ tests/test_scale.py
• uv run pytest tests/test_scale.py::TestIsValidAddress -q
• uv run pre-commit run --all-files
• uv run pytest tests/