security/py-shamir-mnemonic: Add new port

shamir-mnemonic is a Python implementation of SLIP-0039, a standard for
splitting secrets into multiple mnemonic word shares using Shamir's
Secret Sharing scheme.

It is designed primarily for use with cryptocurrency wallets and
hardware devices, enabling secure backup and recovery of sensitive
secrets through human-readable word lists.

The library provides tools for generating mnemonic shares, combining
shares to recover secrets, and validating share sets, while remaining
compatible with SLIP-0039 implementations used by Trezor and related
ecosystems.