rfc6979Nonce

private fn

BigInt rfc6979Nonce(BigInt x,  const(ubyte)[]  digest,
       BigInt q,  size_t qLen,  size_t qBitLen,  HashFactory hashFactory)

Generates a deterministic ECDSA nonce k per RFC 6979 Section 3.2.

This function implements the HMAC-DRBG-based deterministic nonce generation algorithm, producing a predictable k from the private key and message hash. This eliminates the need for a random number generator and ensures reproducible signatures.

Parameters

`x`	The private key scalar.
`digest`	The raw hash output H(m).
`q`	The curve order n.
`qLen`	The byte length of the curve order.
`qBitLen`	The bit length of the curve order.
`hashFactory`	Factory to create hash instances for HMAC.

Returns

The deterministic nonce k in [1, q-1].