feat: add sign_schnorr_no_aux_rand for Keypair

[witter-deland]

#761
kaspanet/rusty-kaspa#586

[apoelstra]

In be017c2:

There is trailing whitespace on multiple lines.

But concept ACK.

[witter-deland]

fixed :)

In be017c2:

There is trailing whitespace on multiple lines.

But concept ACK.

[apoelstra]

In 9f75b63:

There is still a trailing space on line 1017 :)

[witter-deland]

fixed :)

In 9f75b63:

There is still a trailing space on line 1017 :)

[apoelstra]

Please squash these commits.

[witter-deland]

Done, thank you for your patience

Please squash these commits.

[apoelstra]

ACK 2d29116; successfully ran local tests; thanks for iterating!