Support Punycode (RFC 3492)

[dipu-bd]

Add Punycode for internationalized domain names. Low priority — the Bootstring algorithm is complex and unrelated to everything else in the library.

Architecture fit

• Bootstring encoder/decoder — bias adaptation, delta encoding — standalone, shares nothing with the bit engine or radix cores.

Differential oracle: vendor RFC 3492 sample strings (the Arabic/Chinese/etc. worked examples).

Spec: RFC 3492

Effort: L

Checklist

• Bootstring encode/decode with bias adaptation
• RFC 3492 sample strings as known-answer vectors
• Overflow handling verified on node (large deltas)
• README / CHANGELOG / example / test_integration updated
• Format / analyze / test (vm + node) green