refactor: replace Math.log with bit operations for node bits calculation

[m-a-king]

Summary

Refactor the node-bits calculation in TsidFactory.Builder.getNodeBits() by replacing a floating-point logarithm expression with an equivalent integer bit operation.
This change improves clarity and mathematical robustness, and avoids unnecessary floating-point operations in a code path that runs only during factory initialization.

Why a Refactor?

Although the bit-operation approach is theoretically faster, this logic runs only once during startup, so the main motivation is not performance.

Instead, the change aims to:

• remove floating-point precision concerns,
• express the intent (compute required bit width) more directly, and
• align with the library’s existing bit-oriented style.

Testing

The existing testWithNodeCount() test already covers all valid nodeBits cases (0–20), and the new implementation produces identical results, ensuring full backward compatibility.

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Thank you for maintaining this excellent library!
Happy to revise anything if needed.